Catalase Lab Background Information
Practically all of the numerous and complex biochemical reactions that take place in animals, plants,
and microorganisms are regulated by enzymes. Enzymes are proteins. Each enzyme is able to
promote only one type (or a small number) of chemical reaction. Enzymes can be classified into
several broad categories, such as hydrolytic, oxidizing, and reducing, depending on the type of
reaction they control. In an enzyme catalyzed reaction, the compounds on which the enzyme acts are
called substrates and the resulting compounds are called products. Today, we will investigate a
reaction catalyzed by the enzyme Catalase.
The enzyme Catalase carries out the following reaction:
Put in words, Catalase takes two molecules of hydrogen peroxide and converts them to two water
molecules plus a molecule of oxygen gas. Hydrogen peroxide is a toxic molecule (that's why we use it
to kill Bacteria). Hydrogen peroxide is also created in our bodies during normal metabolic events and
catalase is present in the peroxisomes of nearly all human cells. There, it serves to protect the cell
from any toxic effects by catalyzing the decompostion of H2O2 into harmless water and oxygen gas. .
The Catalase protein exists as a dumbbell-shaped tetramer of four identical subunits (220,000 to
350,000 kD). Each monomer contains a heme prosthetic group at the catalytic center. This is the
same type of Heme group as found in Hemoglobin. In the middle of each heme group sits an iron
atom. Catalase uses the iron atom to help it break the bonds in the two molecules of hydrogen
peroxide, shifting the atoms around to release two
molecules of water and a molecule of oxygen gas.
Enzymes have a special affinity for the substrate.
They fit together, matching in shape and charge.
The part of the enzyme where the substrate fits is
called the active site. The amino acid residues in
the active site are in the right 3D conformation to
bind and modify the substrate.
Enzymes are usually more efficient than manmade catalysts operating under the same
conditions. Because many enzymes with different
specificities occur in a cell, each enzyme must be
very efficient. One molecule of the enzyme
catalase, for example, can produce 10*12
molecules of oxygen per second. When hydrogen
peroxide is added to cells containing catalase, the
oxygen gas can actually be seen as it is released
in the form of bubbles!