BOTANY Higher Secondary Second Year - Textbooks Online

Many enzymes consists of a protein and non-protein component. They
are called holoenzymes. The protein component of a holoenzyme is called
apoenzyme and the non-protein component may be inorganic ions such as
Mg 2+ and Mn 2+ . They are tightly attached to apoenzyme. They are called
activators. The non-protein components may be organic substances such
as NAD + , NADP + and FAD + . They are loosely attached to the apoenzyme.
They are called coenzyme or cofactors. An enzyme will not function
without its prosthetic group.
The specific region of the enzyme, which is involved in biochemical
reaction, is termed active site. It is at the active site where the enzyme
combines with its substrates to bring about biochemical reactions. An
enzyme may have more than one active site. They are required only in
very small quantities and yet capable of bringing about changes in large
number of substrate molecules.
5.1.1. Classification of enzymes
Enzymes are classified based on the kinds of reactions they catalyze.
Oxireductase
These enzymes catalyze oxidation or reduction of their substrates by
removing or adding electrons from or to substrates. eg. dehydrogenase,
oxidase and reductase.
Transferase
These enzymes transfer a group from one substrate to other. eg.
transaminase.
Hydrolases
These enzymes split larger molecules into smaller ones by the
hydrolysis of water and breaking of specific covalent bonds. eg.
carbohydrase.
Lyases
These enzymes catalyze the cleavage of specific covalent bonds and
removal of groups without hydrolysis. eg. Histidine decarboxylase.
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