STRUCTURE OF ENZYMES

Enzymes are chemically proteins. Enzymes which are made of only proteins are celled simple enzymes. Eg: Trypsin, Pepsin, Amylase. But some enzymes in addition to their protein structure, have an attached non-protein group. The protein part is called the apoenzyme. Where as the non-protein part is called Co-factor. The complete enzyme is called holoenzyme or conjugated enzyme. In such cases, neither the apoenzyme nor the cofactor is capable of functioning catalytically, if they are not in a combined form. But the co-factor may be identical in several enzymes and therefore particular substrate acted upon by an enzyme is selected by the protein of the enzyme. The co-factor are broadly classified into two types.
1. Prosthetic group:
The firmly bonded co-factor are called prosthetic groups and the loosely bonded organic co-factor are called co-enzymes. When a metal functions as prosthetic group, it is generally referred as an activator. The metal activators have been found to be directly concerned with the catalytic properties of some of the enzymes called active co-factor. Some of the activators are Cu,Fe,Mn,Mg,Zn,Mo,Co. Copper is a co-factor for ascorbic acid oxidases, iron is a co-factor for cytochrome, catalase, perdoxidase xanthine oxidase. Manganese is a co-factor for phosphotransferases, IAA oxidase. Magnesium is a co-factor for Hexokinase, Enolase, G-6-phosphate. Zinc is a co-factor for dehydrogenase, carbonic anhydrase, carboxyl peptidase. Molybdenum is a co-factor for nitrate reductase, dinitrogenase, xanthine oxidase. Cobalt is a co-factor for peptidases. 2. Co-enzyme:
Co-enzyme or secondary substrate act as donors or acceptors or group of atoms that have been added to or removed from the substrate. Some of the co-enzymes include ATP, Co-A, NAD, NADP, Flavin mononucleotide (FMN), Flavin adenine dinucleotide (FAD) etc.

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