A catalyst is defined as any substance that speeds up the rate of a chemical reaction. The compound Manganese Dioxide (MnO2) is an inorganic catalyst for many chemical reactions. Enzymes are proteins that act as organic catalysts.

Hydrogen peroxide (H2O2) is a toxic chemical formed in many cells. Catalase, an enzyme found in many tissues of your body, will break down hydrogen peroxide into water and oxygen as follows:

_catalase

2H₂0₂ -------------------> 2H₂0 + O₂

When this reaction occurs in a test tube, the oxygen gas produced is visible as bubbles! The material being acted upon by the enzyme is called a substrate. View the decomposition of hydrogen peroxide using the inorganic catalyst, manganese dioxide in the video below.

Video 1: The decomposition of H₂O₂ using the inorganic catalyst, MnO₂.

Below is a list of enzyme characteristics:

Enzymes are organic catalysts.
Enzymes are globular proteins. Shape is very important to the active site of an enzyme. The active site of the enzyme recognizes the substrate and binds to the substrate (Fig. 1).
Enzymes are typically highly specific in the reactions they catalyze. Specificity is determined by the active site and its shape, and charge.
Enzymes are not "used up" in the reactions they catalyze.
Enzymes are often named by adding the suffix "ase" to the substrate’s name.
Extremes in pH and high heat will denature enzymes, which is irreversible. Low temperatures can inhibit enzyme activity.
Enzymes can be poisoned by compounds such as cyanide, arsenic, and many other heavy metals. Poisoning permanently alters the enzyme’s active site. Ether, chloroform, and other drugs will inhibit enzyme activity by binding to the active site. When carefully administered, these compounds are used as vehicles or temporary anesthesia.

Enzymes bind to their substrates and their active site.

Figure 1. The induced-fit model is an adjustment to the lock-and-key model and explains how enzymes and substrates undergo dynamic modifications during the transition state to increase the affinity of the substrate for the active site.

As stated in the summary list, a number of variables will affect enzyme activity. In today’s lab you will test various tissues for the presence of catalase and investigate several of the conditions that will alter the activity of this important enzyme.