CLASSIFICATION OF ENZYMES

Enzymes

Enzymes:

Enzymes can be defined as the reaction catalysts of biological systems produced by living cells and are capable of catalyzing chemical reactions. Naturally enzymes are macromolecules having molecular masses ranging into millions. Two exceptional properties of enzymes are their extraordinary specificity — each enzyme catalyzes only one reaction or one group of closely related reactions — and their amazing efficiency — they may speed up reactions by factors of up to 10²⁰. Each enzyme molecule possesses a region known as the active site and the substrate binds itself with this active site. Enzymes are either pure proteins or contain proteins as essential components and in addition require non-proteincomponents which are also essential for their activity. The protein component of the enzyme is called apoenzyme and the non-protein component is called the co-factor or co-enzyme. The co-factorsinclude inorganic ions and complex organic or metallo-organic molecules. Important inorganic co-factors along with their respective enzymes include Fe²⁺ (chrome oxidase) Ze²⁺(carbonic anhydrase) and Mg²⁺ (glucose 6- phosphatase), etc. Many enzymes contain vitamins as their co-factors, for example; nicotinamide adenine dinucleotidecontains nicotinamide vitamin and thiamine pyrophosphatase contains vitamin B₁.

Suffix-"ase" is added to the name of the substrate on which the enzyme acts while naming the enzymes, for example, urease, sucrase, cellulase are the enzymes, which act upon the substrates urea, sucrose and cellulose respectively.

Classification of Enzyme:

Enzymes are classified into six main types by the commission on enzyme, appointed by the International Union of Bio-Chemistry (IUB).

Oxidorednctases:

These are the enzymes which catalyze oxidation-reduction reactions. Common examples are oxidase, dehydrogenase and peroxydase.

Transferases:

These enzymes bring about an exchange of functional group such as phosphate or acyl between two compounds, for example; phospho-transferases, etc.

Hydrolases:

These are the enzymes which catalyze hydrolysis. They include proteasescalled protelytic enzymes.

Lyases:

These are those enzymes which break and form double bonds. They catalyze the addition of ammonia, water or carbon dioxide to double bonds or removalof these to form double bonds, for example phospho-glyceromutases.

Isomerases:

These enzymes catalyze the transfer of groups within molecules to yield isomeric forms of the substrate. An example is the conversion of fumaric acid to maleic acid in the presence offumarase enzyme.

Ligases:

These enzymes are those enzymes which link two molecules together by breaking the high-energy bonds, for example; acetyl—S—COH, a carboxylase and succinic thiokinase.