Enzymes are divided into two groups based on structure. These are-
(i) Simple Enzymes: Enzymes which are made up of proteins only are called simple enzymes. For example, protease, amylase etc.
(ii) Composite Enzymes: Enzymes which are composed of proteins and other substances are called conjugated enzymes. A conjugated enzyme consists of two parts. Protein part and non-protein part. The protein part is called apoenzyme and the non-protein part is called prosthetic group.