Some enzymes only catalyse a reaction if a particular cofactor is present. A cofactor is a non-protein substance that is required by an enzyme for its activity. Some cofactors (prosthetic groups) are a permanently bound, non-protein part of the enzyme’s structure, whereas others form temporary associations with the enzyme (e.g. inorganic ion cofactors and coenzymes).

Inorganic ions

The rate of reaction is increased by the presence of certain ions that may bind to the enzyme or substrate to allow the ESC to form more easily. E.g. Amylase requires chloride ions to function. They may bind to the active site or substrate to alter the charge distribution, or the may bind to an allosteric site on the enzyme, which alters the shape of the active site.

Coenzymes

Small, organic, non-protein molecules that bind temporarily to the active site. They take part in the reaction and are modified but are later recycled and reused. Many coenzymes are derived from vitamins e.g. vitamin B3 is used to make the coenzyme NAD. Lack of enough of a particular vitamin in the diet leads to a deficiency disease. Lack of thiamine causes beriberi whereas lack of vitamin B3 causes pellagra.