### Introduction

Enzymes are molecules that regulate the chemical reactions that occur sin all living organisms. Almost all enzymes are globular proteins that act as catalysts, substances that speed up chemical reactions. Enzymes catalyze reactions by reducing the activation energy for a specific reaction to occur and yet are neither destroyed nor altered during this process. At the molecular level, enzymes catalyze these reactions by briefly binding to the substrate or reactants to form an enzyme-substrate complex. The reaction takes place while the substrate is bound to the enzyme, converting the substrate to the new product. The new product is then released from the enzyme substrate complex and the enzyme is then free to bind with more substrate.

${\text{Enzyme}} + {{\text{Substrate}}} \to {{\text{Enzyme-Substrate Complex}}} \to {\text{Enzyme}} + {{\text{Product}}}$

H2O2 is toxic to most living organisms. Many organisms are capable of enzymatically destroying the H2O2 before it can do much damage. H2O2 can be converted to oxygen and water as follows:

${\text{2}}\ {\text{H}}_{\text{2}}{\text{O}}_{\text{2}}{\text{(aq)}} \to {\text{2}}\ {\text{H}}_{\text{2}}{\text{O}} + {\text{O}}_{\text{2}}{\text{(g)}}$

Although this reaction occurs spontaneously, enzymes increase the rate considerably. At least two different enzymes are known to catalyze this reaction: catalase, found in animals and protists, and peroxidase, found in plants. A great deal can be learned about enzymes by studying the rates of enzyme-catalyzed reactions.

In this Preliminary Activity, you will use a colorimetric assay to determine the rate of reaction of the enzyme peroxidase.

After completing the Preliminary Activity, you will use reference sources to find out more about enzymes, turnips, and peroxidase, and then you will choose and investigate a researchable question. Some topics to consider in your reference search include the following:

• catalyst
• enzyme
• substrate
• peroxidase
• proteins
• denature
• Michaelis-Menten constant
• Lineweaver-Burk plot

### Objectives

In this Preliminary Activity, you will use a spectrophotometer to measure color changes due to the production of dopachrome and determine rate of reaction.

After completing the Preliminary Activity, you will first use reference sources to find out more about enzymes, tyrosine, and tyrosinase before you choose and investigate a researchable question. Some topics to consider in your reference search are:

• catalyst
• enzyme
• substrate
• tyrosine
• tyrosinase
• DOPA
• Michaelis-Menten constant
• Lineweaver-Burk plot