Is there an enzyme that functions without being associated with a complex?

Is there an enzyme that functions without being associated with a complex?

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I'm looking for an enzyme that does not function as part of a complex in its active state. Preferably it also is not part of a kinase or other kind of activating cascade as well though I would appreciate any and all names that are not part of a complex in its active state. Also would be better if it does not require post translational modifications. Of course, pre translational modifications/ interactions at rna or dna level are all good. In eukaryotic genome but bonus points for human genome! Thanks!!


Chosen because the esterase seems like a low energy reaction so it wouldn't need energetic co-factors.

Not sure if I should do a new answer or not.


Our editors will review what you’ve submitted and determine whether to revise the article.

Enzyme, a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process.

What is an enzyme?

  • An enzyme is a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process.
  • The biological processes that occur within all living organisms are chemical reactions, and most are regulated by enzymes.
  • Without enzymes, many of these reactions would not take place at a perceptible rate.
  • Enzymes catalyze all aspects of cell metabolism. This includes the digestion of food, in which large nutrient molecules (such as proteins, carbohydrates, and fats) are broken down into smaller molecules the conservation and transformation of chemical energy and the construction of cellular macromolecules from smaller precursors.
  • Many inherited human diseases, such as albinism and phenylketonuria, result from a deficiency of a particular enzyme.

What are enzymes composed of?

  • A large protein enzyme molecule is composed of one or more amino acid chains called polypeptide chains. The amino acid sequence determines the characteristic folding patterns of the protein’s structure, which is essential to enzyme specificity.
  • If the enzyme is subjected to changes, such as fluctuations in temperature or pH, the protein structure may lose its integrity (denature) and its enzymatic ability.
  • Bound to some enzymes is an additional chemical component called a cofactor, which is a direct participant in the catalytic event and thus is required for enzymatic activity. A cofactor may be either a coenzyme—an organic molecule, such as a vitamin—or an inorganic metal ion. Some enzymes require both.
  • All enzymes were once thought to be proteins, but since the 1980s the catalytic ability of certain nucleic acids, called ribozymes (or catalytic RNAs), has been demonstrated, refuting this axiom.

What are examples of enzymes?

  • Practically all of the numerous and complex biochemical reactions that take place in animals, plants, and microorganisms are regulated by enzymes, and so there are many examples. Among some of the better-known enzymes are the digestive enzymes of animals. The enzyme pepsin, for example, is a critical component of gastric juices, helping to break down food particles in the stomach. Likewise, the enzyme amylase, which is present in saliva, converts starch into sugar, helping to initiate digestion.
  • In medicine, the enzyme thrombin is used to promote wound healing. Other enzymes are used to diagnose certain diseases. The enzyme lysozyme, which destroys cell walls, is used to kill bacteria.
  • The enzyme catalase brings about the reaction by which hydrogen peroxide is decomposed to water and oxygen. Catalase protects cellular organelles and tissues from damage by peroxide, which is continuously produced by metabolic reactions.

What factors affect enzyme activity?

  • Enzyme activity is affected by various factors, including substrate concentration and the presence of inhibiting molecules.
  • The rate of an enzymatic reaction increases with increased substrate concentration, reaching maximum velocity when all active sites of the enzyme molecules are engaged. Thus, enzymatic reaction rate is determined by the speed at which the active sites convert substrate to product.
  • Inhibition of enzyme activity occurs in different ways. Competitive inhibition occurs when molecules similar to the substrate molecules bind to the active site and prevent binding of the actual substrate.
  • Noncompetitive inhibition occurs when an inhibitor binds to the enzyme at a location other than the active site.
  • Another factor affecting enzyme activity is allosteric control, which can involve stimulation of enzyme action as well as inhibition. Allosteric stimulation and inhibition allow production of energy and materials by the cell when they are needed and inhibit production when the supply is adequate.

A brief treatment of enzymes follows. For full treatment, see protein: Enzymes.

The biological processes that occur within all living organisms are chemical reactions, and most are regulated by enzymes. Without enzymes, many of these reactions would not take place at a perceptible rate. Enzymes catalyze all aspects of cell metabolism. This includes the digestion of food, in which large nutrient molecules (such as proteins, carbohydrates, and fats) are broken down into smaller molecules the conservation and transformation of chemical energy and the construction of cellular macromolecules from smaller precursors. Many inherited human diseases, such as albinism and phenylketonuria, result from a deficiency of a particular enzyme.

Enzymes also have valuable industrial and medical applications. The fermenting of wine, leavening of bread, curdling of cheese, and brewing of beer have been practiced from earliest times, but not until the 19th century were these reactions understood to be the result of the catalytic activity of enzymes. Since then, enzymes have assumed an increasing importance in industrial processes that involve organic chemical reactions. The uses of enzymes in medicine include killing disease-causing microorganisms, promoting wound healing, and diagnosing certain diseases.

Electron Transport Chain

The electron transport chain is the final component of aerobic respiration and is the only part of glucose metabolism that uses atmospheric oxygen. Electron transport is a series of redox reactions that resemble a relay race. Electrons are passed rapidly from one component to the next to the endpoint of the chain, where the electrons reduce molecular oxygen, producing water. This requirement for oxygen in the final stages of the chain can be seen in the overall equation for cellular respiration, which requires both glucose and oxygen.

A complex is a structure consisting of a central atom, molecule, or protein weakly connected to surrounding atoms, molecules, or proteins. The electron transport chain is an aggregation of four of these complexes (labeled I through IV), together with associated mobile electron carriers. The electron transport chain is present in multiple copies in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes.

Figure (PageIndex<1>): The electron transport chain: The electron transport chain is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH2 to molecular oxygen. In the process, protons are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water.


There are a variety of health conditions that can interfere with the secretion of sufficient amounts of digestive enzymes for the full digestion of foods. Some are inherited genetic conditions while others develop over time.

Lactose Intolerance

Lactose intolerance is the inability to digest lactose due to insufficient production of lactase by the small intestine. It is characterized by symptoms such as bloating, diarrhea, abdominal pain, and gas that result from consuming milk and other dairy products.   There are several forms of lactose intolerance.

Congenital Lactase Deficiency

Congenital lactase deficiency (also called congenital alactasia) is a rare inherited form of lactose intolerance in which infants are unable to break down lactose in breast milk or formula and have severe diarrhea if they aren't given a lactose-free alternative.

Congenital lactase deficiency is caused by mutations in the LCT gene that provides instructions for making the lactase enzyme.  

Lactase Non-persistence

Lactase non-persistence is a common type of adult-onset lactose intolerance affecting around 65% of adults. It is caused by decreased expression (activity) of the LCT gene. Symptoms typically begin 30 minutes to two hours after ingesting dairy.  

Most people with lactase non-persistence retain some lactase activity and can continue to include some lactose in their diets, such as in the form of cheese or yogurt that tend to be tolerated better than fresh milk.

Secondary Lactose Intolerance

Secondary lactose intolerance develops when lactase production is reduced because of diseases that can cause damage to the small intestine, such as celiac disease or Crohn's disease, or from other illnesses or injuries that impact the intestinal wall.

Exocrine Pancreatic Insufficiency

The pancreas produces the key digestive enzymes of amylase, protease, and lipase. People with exocrine pancreatic insufficiency (EPI) have a deficiency of these enzymes and so are unable to digest food properly, especially fats.

The health conditions that affect the pancreas and are associated with EPI are:

  • Chronic pancreatitis: An inflammation of the pancreas that can permanently damage the organ over time
  • Cystic fibrosis: An inherited genetic condition that causes severe damage to the lungs and digestive system, including the pancreas  
  • Pancreatic cancer


Cellular and Molecular Physiology, Institute of Translational Medicine, University of Liverpool, Liverpool, UK

Michael J. Clague & Sylvie Urbé

Ubiquitin Signalling Division, The Walter and Eliza Hall Institute of Medical Research, Melbourne, Australia

Department of Medical Biology, The University of Melbourne, Melbourne, VIC, 3010, Australia

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar

You can also search for this author in PubMed Google Scholar


M.J.C. wrote the manuscript with input from D.K. and S.U. S.U. prepared original figures. All authors read and discussed the manuscript and responded to reviewers.

Corresponding authors

Enzymes and human body

Enzymes have a great diversity of functions that range from signal transduction to stimulate movements, such as myosin to hydrolyze ATP, in order to produce muscle contraction in the gallbladder. They also help the division of molecules, such as transferase, and the regulation of some biological processes in the body.

Three large groups of enzymes are known in the human body, these are:

Metabolic enzymes are those enzymes that are present in all organs and systems of the human body, making possible chemical reactions in the body’s cells.

Two of the most important enzymes during the process are dismutase, which acts as an antioxidant and catalase, responsible for breaking down hydrogen peroxide.

However, it is important to clarify that there are many other enzymes that possess cellular functions.

Food or food enzymes are all those enzymes found in foods of animal or plant origin, such as lipase, cellulase, protease and amylase.

These types of enzymes have active units that favor the process of decomposition of proteins, fats and carbohydrates in the body. Similarly, they favor the digestive system and stimulate the production of metabolic enzymes in the human body.

Some enzymes of animal origin even act as anti-inflammatory, improve digestion as is the case with bromelain and pepsin.

There are enzymes such as renin, capable of preparing milk for the management of lipase and pepsin. You are responsible for making chemical reactions possible in the human body.

There are others such as trypsin restricts arginine or lysine, which is activated before alkaline ph.

This digestive enzymes receive such a name because, once they are secreted by the body, they have the ability to help during the digestion process of the food we consume daily.

Such is the case of proteases, responsible for the digestion of proteins. These types of enzymes are usually found in pancreatic, gastric and intestinal juices.

Another of the enzymes involved during the digestive process is amylase, which is responsible for breaking down carbohydrates. It usually comes from the pancreas, saliva and intestine.

Lipase is produced in the stomach and is responsible for digesting fats.

Amylase, produced by the salivary glands during chewing and by the pancreas, is responsible for destroying the bonds between carbohydrate molecules, generating disaccharides and trisaccharides, while converting starch into maltose.

Enzyme Activity Review in 26 Easy Questions

Catalysts are substances that reduce the activation energy of a chemical reaction, facilitating it or making it energetically viable. The catalyst increases the speed of the chemical reaction.

More Bite-Sized Q&As Below

2. What amount of catalyst is consumed in the reaction it catalyzes?

Catalysts are not consumed in the reactions they catalyze.

3. Is there a difference between the initial and the final energy levels in catalyzed and non-catalyzed reactions?

The catalysis does not alter the state of the energy of the reagents and products of a chemical reaction. Only the energy necessary for the reaction to occur, that is, the activation energy, is altered.

4. What are enzymes? What is the importance of enzymes for living beings?

Enzymes are proteins that are catalysts of chemical reactions. Chemistry shows us that catalysts are non-consumable substances that reduce the activation energy necessary for a chemical reaction to occur.

Enzymes are highly specific to the reactions they catalyze. They are of vital importance for life because most of the chemical reactions in cells and tissues are catalyzed by enzymes. Without enzyme action, those reactions would not occur or would not happen with the required speed for the biological processes in which they are involved.

The Enzyme-Substrate Complex

5. What are substrates of enzymatic reactions?

Substrates are reagent molecules upon which enzymes act.

Enzymes have spatial binding sites to attach to their substrate. These sites are called the activation centers of the enzyme. Substrates bind to these centers, forming the enzyme-substrate complex.

6. What are the main theoretical models that try to explain the formation of the enzyme-substrate complex?

There are two main models that explain the formation of the enzyme-substrate complex: the lock and key model and the induced fit model.

In the lock and key model, the enzyme has a region with a specific spatial conformation for the binding of the substrate. In the induced fit model, the binding of the substrate induces a change in the spatial configuration of the enzyme to make the substrate fit.

7. How does the formation of the enzyme-substrate complex explain the reduction in the activation energy of chemical reactions?

The enzyme possibly works as like a test tube within which reagents meet to form products. Enzymes facilitate this meeting, making it easier for collisions between reagents to occur and, as a result, the activation energy of the chemical reaction is reduced. This is one possible hypothesis.

8. On what structural level of the enzyme (primary, secondary, tertiary or quaternary) does the enzyme-substrate interaction depend?

The substrate binds to the enzyme at the activation centers. These are specific three-dimensional sites and therefore they depend on the protein's tertiary and quaternary structures. The primary and secondary structures, however, condition the other structures, and consequently are equally important.

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Specificity of Enzymatic Action

9. What is the activation center of an enzyme? Is it the key or the lock in the lock and key model?

The activation center is a region of the enzyme produced by its spatial conformation to which the substrate binds. In the lock and key model, the activation center is the lock and the substrate is the key.

10. Why enzyme action is considered highly specific?

Enzyme action is highly specific because only the specific substrates of an enzyme bind to the activation center of that enzyme. Each enzyme generally catalyzes only one specific chemical reaction.

Factors that Change Enzyme Activity

11. What happens to the functionality of a denatured enzyme? How can that result be explained with the help of the lock and key model?

According to the lock and key, enzyme functionality depends entirely on the integrity of the activation center, a molecular region with specific spatial characteristics. After denaturation, the spatial conformation of the protein is modified, the activation center is destroyed and the enzyme loses its catalytic activity.

12. What are the main factors that alter the speed of enzymatic reactions?

The main factors that change the speed of enzymatic reactions are temperature, pH and substrate concentration (quantity).

13. How does substrate concentration affect the speed of enzymatic reactions?

Initially, as substrate concentration increases, the speed of the reaction increases. This happens because free activation centers of the enzyme bind to free substrates. Once all the activation centers of the available enzymes are bound to their substrates, new increases in the substrate concentration will have no effect on the speed of the reaction.

14. How does temperature affect the action of enzymes on their substrates?

There are defined temperature ranges under which enzymes operate and there is a specific temperature level (optimum temperature) in which enzymes have maximum efficiency. Therefore, temperature variations affect enzyme activity and the speed of the reactions they catalyze.

In addition, because they are proteins, enzymes can be denatured under extreme temperatures.

15. Concerning enzymatic reactions, how different are the curves of the graph of the variation in the speed of a reaction as function of substrate concentration and the graph of the variation in the speed of a reaction as function of temperature?

The curve of the variation in speed of the enzymatic reaction as a function of increasing substrate concentration increases in a curve formation until approaching the point where it stabilizes due to the saturation of the activationꃎnters of the enzymes.

The curve of the variation in the speed of the enzymatic reaction as a function of increasing temperature initially increases and then reaches a peak (the optimum temperature), after which it decreases to zero at the point in which the enzymes are rendered inactive by denaturation.

16. What is the relationship between  the cooling of organs and tissues for medical transplants and the effect of temperature on enzymatic reactions?

Molecular degradation during the decomposition of organs and tissues is catalyzed by enzymes. The cooling to adequate temperatures of some organs and tissues destined for transplantation reduces that enzyme activity and thus decreases the natural decomposition process. By the same rationale, the cooling reduces the metabolic work of cells and prevents the breakdown of their own structures to obtain energy. A subsequent increase in temperature reverts the denaturation of enzymes, allowing the organs and tissues also preserved by other specific techniques to be grafted into the receptors.

17. Does pH affect enzyme activity?

The concentration of hydrogen ions in a solution affects enzyme activity. Each enzyme has a maximum efficiency in an optimum pH.

Since pH is one of the factors in the denaturation of proteins, if an enzyme is subject to a pH level under which it is denatured, there will be no enzymatic activity.

18. Do enzymes act better under acidic or alkaline pHs?

Most enzymes act under pHs between 6 and 8, a range that corresponds to the general acidic level of cells and blood. There are enzymes, however, that act only under very acid or very alkaline pH. Therefore, enzyme activity depends on pH range.

In the stomach, for example, gastric juice has a very low pH, around 2. Nonetheless, the enzyme pepsin acts to intensively digest proteins. In the duodenum, pancreatic secretions increase the pH of the intestinal juice to allow other digestive enzymes, such as trypsin, to act.

19. Since pepsin is a gastric enzyme, does it have an acidic or alkaline optimum pH? What happens to pepsin when it enters the duodenum?

Pepsin acts within the stomach so its optimum pH is around 2, an acidic pH. When the enzyme enters the duodenum, it comes in contact with a higher pH and its enzyme activity comes to and end.


20. What are enzyme cofactors?

Some enzymes need other associated molecules to work. These molecules are called enzyme cofactors and they can be organic ions like mineral salts, or organic molecules, to give some examples.

Inactive enzymes which are not bound to their cofactors are called apoenzymes. Active enzymes bound to their cofactors are called holoenzymes.

21. What is the relationship between vitamins and enzyme cofactors?

Many vitamins are enzyme cofactors that cannot be synthesized by the body and, as a result, must be obtained from the diet.

Enzyme Inhibitors, Allosterism and Zymogens

22. In a enzymatic reaction, what is the effect of a substance with the same spatial conformation as the enzyme substrate? How is this type of substance recognized?

Substances that “simulate” substrates can bind to the activation center of enzymes, thus blocking the true substrates from binding to these enzymes and paralyzing the enzymatic reaction. These “fake substrates” are called enzyme inhibitors.

The binding of enzyme inhibitors to enzymes can be reversible or irreversible.

Many medical drugs, including some antibiotics, antivirals, antineoplastics, antihypertensives and even sildenafil (trade name Viagra), are enzyme inhibitors that block enzyme activity.

23. What is the mechanism of action of the antibiotic penicillin?

Penicillin, discovered by the Scottish doctor Alexander Fleming in 1928, is a drug that inhibits the enzymes necessary for the synthesis of peptidoglycans, a component of the bacterial cell wall. Through this, the inhibition the bacterial population stops growing because there is no new cell wall formation.

Fleming won the Nobel Prize in medicine for the discovery of penicillin.

24. What is the mechanism of action of the antiretroviral drugs called protease inhibitors which are used against HIV infection?

Protease inhibitors are some of the antiretroviral drugs used to treat HIV infection. Protease is an enzyme necessary for the construction of the  human immunodeficiency virus (HIV)ꂯter the synthesis of its proteins within the host cell. The protease inhibitor binds to the activation center of the enzyme blocking the formation of the enzyme-substrate complex and enzyme activity, thus stopping viral replication.

25. What are allosteric enzymes?

Allosteric enzymes are enzymes with more than one activation center and to which other substances, called allosteric regulators, bind.

Allosteric regulators can be allosteric inhibitors or allosteric activators. The interaction between an allosteric enzyme and an allosteric inhibitor prohibits the binding of the substrate to the enzyme. The interaction between an allosteric enzyme and an allosteric activator allows the binding of the substrate to the enzyme and sometimes increases the affinity of the enzyme for the substrate. This regulatory phenomenon of enzyme activity is called allosterism.

26. What are zymogens?

Zymogens, or proenzymes, are enzymes secreted in inactive form. Under certain conditions, a zymogen changes into the active form of the enzyme. In general, zymogen secretions happen because enzyme activity can harm secretory tissue.

For example, the pepsinogen secreted by the stomach becomes active under an acidic pH, turning into the enzyme pepsin. Other well-known zymogens are trypsinogen and chymotrypsinogen, enzymes that are secreted by the exocrine pancreas and which become trypsin and chymotrypsin respectively.

Enzyme Basics

Enzymes permit a vast number of reactions to take place in the body under conditions of homeostasis, or overall biochemical balance. For example, many enzymes function best at a pH (acidity) level close to the pH the body normally maintains, which is in the range of 7 (that is, neither alkaline nor acidic). Other enzymes function best at low pH (high acidity) because of the demands of their environment for example, the inside of the stomach, where some digestive enzymes operate, is highly acidic.

Enzymes take part in processes ranging from blood clotting to DNA synthesis to digestion. Some are found only within cells and participate in processes involving small molecules, such as glycolysis others are secreted directly into the gut and act on bulk matter such as swallowed food.

Because enzymes are proteins with fairly high molecular masses, they each have a distinct three-dimensional shape. This determines the specific molecules on which they act. In addition to being pH-dependent, the shape of most enzymes is temperature-dependent, meaning that they function best in a fairly narrow temperature range.


Protease enzymes are secreted by the stomach, pancreas and small intestine and their job is to digest proteins. An example of a protease is pepsin which is secreted in the stomach. Proteins are long chains of amino acids, and protease enzymes break them into peptides (smaller chains of amino acids molecules) and eventually into individual amino acids, which are small and easily absorbed in the small intestine. The word equation for the protease reaction is:

AP Sample Lab 2 Catalysis 2

Enzymes are proteins produced by living cells. They are biochemical catalysts meaning they lower the activation energy needed for a biochemical reaction to occur. Because of enzyme activity, cells can carry out complex chemical activities at relatively low temperatures. The substrate is the substance acted upon in an enzyme-catalyzed reaction, and it can bind reversibly to the active site of the enzyme. The active site is the portion of the enzyme that interacts with the substrate so that any substrate that blocks or changes the shape of the active sit effects the activity of the enzyme. The result of this temporary union is a reduction in the amount of energy required to activate the reaction of the substrate molecule so that products are formed. The following equation demonstrates this process: E + S ↔ ES ↔ E + P Enzymes follow the law of mass reaction. Therefore, the enzyme is not changed in the reaction and can be recycled to break down additional substrate molecules.

Several factors can affect the action of an enzyme: salt concentration, pH of the environment, temperature, activations and inhibitors. If salt concentration is close to zero, the changed amino acid side chains of the enzyme molecules will attract one another. The enzyme will then denature and form an inactive precipitate. Denaturation occurs when excess heat destroys the tertiary structure of proteins. This usually occurs at 40 to 50º Celsius. If salt concentration is high, the normal interaction of charged groups will be blocked. An intermediate salt concentration is normally the optimum for enzyme activity. The salt concentration of blood and cytoplasm are good examples of intermediate concentrations. The pH scale is a logarithmic scale that measures the acidity or H+ concentration in a solution and runs from 0 to 14, with 0 being highest in acidity and 14 lowest. Amino acid side chains contain groups such as –COOH that readily gain or lose H+ ions. As the pH is lowered an enzyme will tend to gain H+ ions, disrupting the enzyme’s shape. If the pH is raised, the enzyme will lose H+ ions and eventually lose its active shape. Reactions usually perform optimally in neutral environments. Chemical reactions generally speed up as the temperature is raised. More of the reacting molecules have enough kinetic energy to undergo the reaction as the temperature increases. However, if the temperature goes above the temperature optimum, the conformation of the enzyme molecules is disrupted. An activator is a coenzyme that increases the rate of the reaction and can regulate how fast the enzyme acts. It also makes the active site a better fit for the substrate. An inhibitor has the same power of activator regulation but decrease the reaction rate. An inhibitor also reduces the number of S-S bridges and reacts with the side chains near activation sites, blocking them.

The enzyme used in this lab is catalase. It has four polypeptide chains that are each composed of more than 500 amino acids. One catalase function is to prevent the accumulation of toxic levels of hydrogen peroxide formed as a by-product of metabolic processes. Many oxidation reactions that occur in cells involve catalase. The following is the primary reaction catalyzed by catalase, the decomposition of hydrogen peroxide to form water and oxygen:

2 H2O2 → 2 H2O + O2 (gas) Without catalase this reaction occurs spontaneously but very slowly. Catalase speeds up the reaction notably.

The direction of an enzyme-catalyzed reaction is directly dependent on the concentration of enzyme, substrate, and product. For example, lots of substrate with a little product makes more product. Another example is lots of product with a little enzyme forms more substrate. Much can be learned about enzymes by studying the kinetics of enzyme-catalyzed reaction. It is possible to measure the amount of product formed, or the amount of substrate used, from the moment the reactants are brought together until the reaction has stopped.

Enzyme catalase, when working under optimum conditions, noticeably increases the rate of hydrogen peroxide decomposition.

The materials needed for exercise 2A of the lab are: 30 mL of 1.5% (0.44 M) H2O2, a 50- mL glass beaker, 6 mL of freshly made catalase solution, a test tube, boiling water bath, 1 cm³ of liver, a knife for maceration, paper towels, safety goggles, lab apron, pencil, eraser, and paper to record results.

The materials needed for exercise 2B are: 10 mL of 1.5% H2O2, two clean glass beakers, 1 mL of H2O, 10 mL of H2SO4, a white sheet of paper, a 5 mL syringe, approximately 5 mL of KMnO4, paper, pencil, eraser, safety goggles, and lab aprons.

The materials needed for exercise 2C of the lab are: 20 mL of 1.5% H2O2, two glass beakers, 1 mL of H2O, 10 mL of H2SO4, a white sheet of paper, a 5 mL syringe, approximately 5 mL of KMnO4, paper, pencil, eraser, safety goggles, and lab aprons.

For this part of the experiment, the materials needed are 12 cups labeled 10, 30, 60, 120, 180, and 360 on two each, six cups labeled acid, 60 mL of 1.5% H2O2, a clean 50-mL beaker, 6 mL of catalase extract, two 5-mL syringes, KMnO4, a timer, paper, pencil, black marker, eraser, safety goggles, and lab aprons.

Transfer 10 mL of 1.5% H2O2 into a 50-mL glass beaker and add 1 mL of freshly made catalase solution. Remember to keep the catalase solution on ice at all times. Record the results. Then transfer 5 mL of purified catalase extract to a test tube and place it in a boiling water bath for five minutes. Transfer 10 mL of 1.5% H2O2 into a 50-mL beaker and add 1 mL of the cooled, boiled catalase solution. Again record the results. To demonstrate the presence of catalase in living tissue, cut 1 cm of liver, macerate it, and transfer it into a 50-mL glass beaker containing 10 mL of 1.5% H2O2. Record these results.

Put 10 ml of 1.5% H2O2 into a clean glass beaker. Add 1 mL of H2O. Add 10 mL of H2SO4 (1.0 M) using extreme caution. Mix this solution well. Remove a 5 mL sample and place it into another beaker. Assay for the amount of H2O2 as follows. Place the beaker containing the sample over white paper. Use a 5-mL syringe to add KMnO4 a drop at a time to the solution until a persistent pink or brown color is obtained. Remember to gently swirl the solution after adding each drop. Record all results. Check with another group before proceeding to see that results are similar.

To determine the rate of spontaneous conversion of H2O2 to H2O and O2 in an uncatalyzed reaction, put about 20 mL of 1.5% H2O2 in a beaker. Store it uncovered at room temperature for approximately 24 hours. Repeat the steps from Exercise 2B, using the uncatalyzed H2O2, to determine the proportional amount H2O2 of remaining after 24 hours. Record the results.

If a day or more has passed since Exercise B was performed, it is necessary to reestablish the baseline. Repeat the assay and record the results. Compare with other groups to check that results are similar. To determine the course of an enzymatic reaction, how much substrate is disappearing over time must be measured. First, set up the cups with the times and the word acid up. Add 10 mL of H2SO4 to each of the cups marked acid. Then put 10 mL of 1.5% H2O2 into the cup marked 10 sec. Add 1 mL of catalase extract to this cup. Swirl gently for 10 seconds. (Calculate time using the timer for accuracy.) At 10 seconds, add the contents of one of the acid filled cups. Remove 5 mL and place in the second cup marked 10 sec. Assay the 5-mL sample by adding KMnO4 a drop at a time until the solution obtains a pink or brown color. Repeat the above steps except allow the reactions to proceed for 30, 60, 120, 180, and 360 seconds, respectively. Use the times’ corresponding, marked cups. Record all results and observations.

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