Enzymes and their functions

Enzymes are the biocatalysts of life. They are defined as biocatalysts synthesized by living cells. They are simple or conjugate protein and specific in action. At present about 300 enzymes are recognized and classified into six classes by International Union of Biochemistry (IUB). They are: Oxidoreductases, Transferases, Hydrolases, Lyases, Isomerases and Ligases. However about ~10% i.e., 300 enzymes are commercially available.

The enzyme facilities a biochemical reaction by providing alternative lower activation energy pathways thereby increasing the rate of reaction. Enzymes being proteins having colloidal nature often get inactivated during reactions and have to be constantly replaced by synthesis in the body.

The functional unit of enzymes is called 'Holoenzyme'. This is made up of 'apoenzyme' which is a protein part and a non protein part called prosthetic group. The prosthetic group which is covalently attached with the enzyme is known as cofactor.

Apoenzyme + Co-enzyme Holoenzyne

(protein part) (Non protein part) (Active enzyme)

The prosthetic groups which get attached to the enzyme at the time of reaction are known as coenzymes.

Active site of an enzyme binds the substrate and forms Enzyme substrate complex. Active site is a small region on enzyme at which the substrate binds and participates in catalysis. The enzyme substrate complex formed release enzymes and products. Thus the free enzyme is available for reuse.

The enzymatic reaction proceeds this four stages.

i) Formation of complex between enzyme and substitute (ES)

ii) Conversion of this complex to in enzyme-intermediate complex (EI)

iii) Further conversion to a complex between enzyme and product (EP)

iv) Dissociation of the enzyme - product complex, leaving the enzyme unchanged.

Functions of Enzymes

• Enzymes control several metabolic pathways and are highly specific in their action.

• Enzymes like invertase, zymase and maltase are used in manufacture of alcoholic drinks.

• Some enzymes are used as therapeutic agents. For e.g., streptokinase is used to dissolve blood clots. Asparginase is used for treatment of leukaemia.

• As the activity of enzyme decreases, the temperature of the body also decreased.

• Enzymes enhance rate of reaction through acid-base catalysis and covalent catalysis.

• Estimation of serum enzymes helps in the right diagnosis of a particular disease.

Deficiency symptoms

Deficiency of some enzymes causes diseases like albinism in individuals.

Albinism is caused due to the deficiency of enzyme tyrosinase.

Phenyl ketonuria is caused due to the deficiency of enzyme phenyl alanine hydroxylase.