Enzymes are macromolecular biological catalysts. Enzymes accelerate chemical reactions. The molecules upon which enzymes may act are called substrates and the enzyme converts the substrates into different molecules known as products.

Enzymesare the biocatalysts with high molecular weight proteinous compound. It enhances the reactions which occur in the body during various life processes.It helpsthe substrate by providingthe surface for the reaction to occur. The enzyme comprises of hollow spaces occupying groups such as -SH, -COOH, etc., on the outer surface. The substrate which has the opposite charge of the enzyme fits into these spaces just like key fits into a lock. This substrate binding site is called the active site of an enzyme (E).Once substrate (S) binds to this active site, they form a complex (intermediate-ES) which then produces the product (P) and the enzyme (E) The substrate which gets attached to the enzyme has a specific structure and that can only fit in a particular enzyme. Hence by providing a surface for the substrate, an enzyme slows down the activation energy of the reaction. The intermediate state where the substrate binds to the enzyme is called the transition state. By breaking and making the bonds, the substrate binds to the enzyme (remains unchanged), converts into the product and later splits into product and enzyme. The free enzymes then bind to other substrates and the catalytic cycle continues until the reaction completes.

The enzyme action basically happens in two steps:

Step1:Combining of enzyme and the reactant/substrate.

E+S → [ES]

Step 2:Disintegration of the complex molecule to give the product.

[ES]→E+P

Thus, the whole catalyst action of enzymes is summarized as:

E + S →[ES] →[EP] → E+ P