Enzymes are naturally occurring simple conjugate proteins acting as specific catalysts in all processes. In contrast to ordinary chemical catalyst, it loses activity by pH or temperature change.

For example:- the enzyme used to catalyze the hydrolysis of maltose into glucose is named as maltase.

Enzymes are highly specific, i.e., a particular enzyme catalyses a specific reaction. For example, urase attacks on urea. This specific action is due to active sites present in the enzyme molecule (E) that fits into substrate (S) and forms E-S complex which changes into product P and E.

Enzymes increase the speed of reactions. They can catalyze several million of reactions per second.