Enzymes are generally classified on the basis of the type of reactions that they catalyse. 6 groups of enzymes can be recognised on this basis. The following table lists the 6 groups of enzymes along with example.
fig. 14.15 - Classification of Enzymes
Enzymes get denatured at very high temperatures, above 650C. This denaturing occurs due to breakdown of the protein molecule.
Any chemical substance which has a molecular structure that closely resembles a substrate, can reduce or inhibit the activity of an enzyme. Such an inhibitor is called competitive inhibitor. This situation is comparable to a lock jammed by a key almost similar to the original one.
fig. 14.16 - Competitive Inhibition
Chemical substances such as cyanides or phosphide can inhibit the action of repiratory enzymes. They are not similar to the substrate molecule and as such do not compete with it. However, such inhibitor may become attached any site on the enzyme, other than the substrate binding site.
fig. 14.17 - Noncompetitive Inhibition
The activity of some enzymes, particularly those involved in metabolic pathways, are controlled by a self-regulating mechanism. Some specific substance, most often the product itself, acts as an inhibitor. Such an inhibitor binds to an enzyme at a specific site and modifies the active site of the enzyme. This prevents the binding of substrate molecule. Such sites on the enzymes are called allosteric sites and such enzymes are called allosteric enzymes.
fig. 14.18 - Allosteric Inhibition