Enzyme Cofactors

Many enzymes require non-protein helper components, called cofactors, for efficient catalytic activity. Cofactors range from simple inorganic ions to relatively complex organic molecules, and are grouped into three types: inorganic ions, prosthetic groups and coenzymes. The complete, catalytically active enzyme - protein plus its bound cofactor - is called a holoenzyme; the inactive protein portion alone, without its cofactor, is called an apoenzyme. Inorganic ions help increase the rate of the reaction an enzyme catalyses - for example, salivary amylase activity is enhanced in the presence of chloride ions. Prosthetic groups are organic molecules that assist an enzyme's catalytic function and typically remain tightly and permanently bound to it; examples include flavin adenine dinucleotide (FAD), which contains riboflavin (vitamin B2) and functions to accept hydrogen atoms during redox reactions, and 'haem', an iron-containing prosthetic group with a central iron atom, found in enzymes like catalase and in oxygen-carrying proteins. Coenzymes are organic compounds that also act as cofactors, but - unlike prosthetic groups - do not remain permanently attached to the enzyme; many essential coenzymes are built from vitamins, and examples include NAD, NADP, coenzyme A and …