WHAT ARE ENZYMES

 WHAT ARE ENZYMES?

Enzymes are biological catalysts. They increase the rate of chemical reactions taking

place within living cells without themselves suffering any overall change. The

reactants of enzyme-catalysed reactions are termed substrates. Each enzyme is

quite specific in character, acting on a particular substrate or substrates to produce a

particular product or products.

All enzymes are proteins. However, without the presence of a non-protein

component called a cofactor, many enzyme proteins lack catalytic activity. When

this is the case, the inactive protein component of an enzyme is termed the

apoenzyme, and the active enzyme, including cofactor, the holoenzyme. The

cofactor may be an organic molecule, when it is known as a coenzyme, or it may be

a metal ion. Some enzymes bind cofactors more tightly than others. When a cofactor

is bound so tightly that it is difficult to remove without damaging the enzyme, it is

sometimes called a prosthetic group.

To summarize diagrammatically:

CO-ENZYME < INACTIVE-PROTEIN+ACTIVE PROTEIN+COFACTOR < METAL ION+COENZYME 

As we shall see later, both the protein and cofactor components may be directly

involved in the catalytic processes taking place.