Enzymes, commonly known as biocatalysts, are unique and highly specific globular proteins.
They accelerate chemical reactions without themselves undergoing any apparent change during the process.
They are produced within the cells but are capable of action outside the cells. The word ‘enzyme’ was first introduced by Kuhne in 1878. Each enzyme usually acts on a single substrate and is said to be highly specific in its action.
According to lock and key hypothesis, the substrate molecules fit into the active sites located on the surface of the enzyme molecules just as one particular key fits into one particular lock.
These results in the formation of intermediate compounds called enzyme -substrate complexes by reversible reaction enzyme + substrate enzyme – substrate complex. These compounds are less stable than the original substrate and so they break down spontaneously, the enzyme being again liberated. According to their chemical reactions, enzymes are classified into 6 major divisions:
These enzymes allow oxidation or reduction reactions; removal or addition of hydrogen atoms. They are essential for both aerobic and anaerobic respirations, e.g., dehydrogenase, peroxidase and oxidase.
Theseenzymescatalyzethe transfer of specific group from one substance to another, e.g., transaminases, transphosphorylases and kinases.
These enzymes bring about the hydrolysis or condensation of substrates by the addition or removal of water, e.g., phosphatases, peptidases, amidases, pepsin, trypsin, erepsin, etc.
These enzymes catalyze the removal of groups from substrates non-hydrolytically, e.g., fumarase, decarboxylase and aldolase.
These enzymes catalyze intramolecular rearrangement, e.g., triose phosphate isomerase.
These enzymes catalyze the union of two molecules, coupled with the breakdown of a pyrophosphate bond, e.g., X: Y ligase and acetylcoenzyme.