Enzymes are the catalysts of biological systems. They speed up chemical reactions in biological systems by lowering the activation energy, the energy needed for molecules to begin reacting with each other. Enzymes do this by forming an enzyme-substrate complex that reduces energy required for the specific reaction to occur. Enzymes have specific shapes and structures that determine their functions. The enzyme’s active site is very selective, allowing only certain substances to bind. If the shape of an enzyme is changed in any way, or the protein denatured, then the binding site also changes, thus disrupting enzymatic functions.
Enzymes are fundamental to the survival of any living system and are organized into a number of groups depending on their specific activities. Two common groups are catabolic enzymes (“cata” or “kata-” from the Greek “to break down”) — for instance, amylase breaks complex starches into simple sugars — and anabolic enzymes (“a-” or “an-” from the Greek “to build up”). (You may know this second word already from stories about athletes who have been caught using anabolic steroids to build muscle.)
Catalytic enzymes, called proteases, break down proteins and are found in many organisms; one example is bromelain, which comes from pineapple and can break down gelatin. Bromelain often is an ingredient in commercial meat marinades. Papain is an enzyme that comes from papaya and is used in some teeth whiteners to break down the bacterial film on teeth. People who are lactose intolerant cannot digest milk sugar (lactose); however, they can take supplements containing lactase, the enzyme they are missing. All of these enzymes hydrolyze large, complex molecules into their simpler components; bromelain and papain break proteins down to amino acids, while lactase breaks lactose down to simpler sugars.
Anabolic enzymes are equally vital to all living systems. One example is ATP synthase, the enzyme that stores cellular energy in ATP by combining ADP and phosphate. Another example is rubisco, an enzyme involved in the anabolic reactions of building sugar molecules in the Calvin cycle of photosynthesis.
• To understand the relationship between enzyme structure and function
• To make some generalizations about enzymes by studying just one enzyme in particular
• To determine which factors can change the rate of an enzyme reaction
• To determine which factors that affect enzyme activity could be biologically important
Developing a Method for Measuring Catalase (also called Peroxidase)
Peroxide (such as hydrogen peroxide) is a toxic byproduct of aerobic metabolism. Catalase is an enzyme that breaks down these peroxides. It is produced by most cells in their peroxisomes.
The general reaction can be depicted as follows:
Enzyme + Substrate --> Enzyme-Substrate Complex --> Enzyme + Product(s) + ΔG
For this investigation the specific reaction is as follows:
Catalase + Hydrogen Peroxide --> Complex --> Catalase + Water + Oxygen
2H2O2 → 2H2O + O2 (gas)
Notice that the catalase is present at the start and end of the reaction. Like all catalysts, enzymes are not consumed by the reactions. To determine the rate of an enzymatic reaction, you must measure a change in the amount of at least one specific substrate or product over time. In a decomposition reaction of peroxide by catalase (as noted in the above formula), the easiest molecule to measure would probably be oxygen, a final product.
Let’s look at the set up for measuring the disappearance of the substrate, H2O2 during a timed trial.
As catalase converts H2O2 to water and oxygen, the concentration of H2O2 decreases. Before all the H2O2 is converted to product, the reaction is stopped by adding sulfuric acid (H2SO4). After the reaction is stopped, the amount of substrate (H2O2) remaining in the beaker is measured. Potassium