OANA NAFORNITA & WENDELA BIRGERSSON

CATALASE

Catalase is a common enzyme found in nearly all living organisms exposed to oxygen. It catalyzes the decomposition of hydrogen peroxide to water and oxygen.

It is a very important enzyme in reproductive reactions and has one of the highest turnover numbers of all enzymes; one catalase molecule can convert millions of molecules of hydrogen peroxide to water and oxygen each second.

Catalase is used in the food industry for removing hydrogen peroxide from milk prior to cheese production. Another use is in food wrappers where it prevents food from oxidizing. Catalase is also used in the textile industry, removing hydrogen peroxide from fabrics to make sure the material is peroxide-free

Catalase was first noticed in 1811 when Louis Jacques Thénard, who discovered hydrogen peroxide, suggested its breakdown is caused by an unknown substance. In 1900, Oscar Loew was the first to give it the name catalase, and found it in many plants and animals.

In 1969, the amino acid sequence of bovine catalase was worked out. Then in 1981, the three-dimensional structure of the protein was revealed.

PRIMARY STRUCTURE

The primary structure of catalase consists of apolypeptide chain made up of 506 amino acids, one heme group and one NADH molecule.

SECONDARY STRUCTUREOnly about 60% of catalase structure is composed of regular secondary structural motifs: a-helices account for 26% of its structure and b-structure for 12%. Irregular structure includes a predominance of extended single stands and loops that play a major role in the assembly of the tetramer.

TERTIARY STRUCTUREThe tertiary structure is globular and is held together with disulphide bridges and hydrogen bonds. This globular structure is the one which makes catalase soluble in water.

QUATERNARY STRUCTUREThe quaternary structure comprises four monomer sub-units. Each monomer has a porphyrin heme group and a NADPH molecule. Porphyrin is made up of a photoporphyrin ring and central iron (Fe) atom.

RELATION BETWEEN STRUCTURE AND FUNCTION

An increase in the concentration of substrate would cause an increase in the rate of catalase activity because of a larger chance that catalase enzymes will collide with hydrogen peroxide molecules and the active site reacting with the hydrogen peroxide.

The rate of reaction doubles as the concentration of hydrogen peroxide doubles because there are twice the number of substrate molecules so the active sites are twice as likely to collide with a substrate molecule.

According to recent scientific studies, low levels of catalase may play a role in the graying process of human hair. Hydrogen peroxide is naturally produced by the body and catalase breaks it down. If catalase levels decline, hydrogen peroxide cannot be broken down as well. This allows the hydrogen peroxide to bleach the hair from the inside out. This finding may someday be incorporated into treatments for graying hair