Coenzymes

Coenzymes are organic molecules that are needed for the proper functioning of enzymes.Many co-enzymes are synthesised from vitamins taken in the diet.For example vitamin B3 is used to make NAD (nicotinamide adenine dinucleotide) which is needed for respiration and vitamin B5 is needed to make coenzyme A which is also needed for respiration.Coenzymes are usually needed to carry the products of the reaction.Coenzymes themselves may be changed in the reaction, but are then regenerated so they can be used again.An example is the enzyme lactate dehydrogenase, for which the coenzyme is nicotinamide adenine dinucleotide (NAD).In the dehydrogenation reaction of lactate to pyruvate, NAD accepts hydrogen and itself becomes reduced. Reduced NAD then becomes oxidised by transferring the hydrogen to another protein.NAD is derived from vitamins of the B3.Other vitamins found in coenzymes are pantothenic acid, ascorbic acid, tetrahydrofolate, pyridoxal phosphate and thiamine pyrophosphate.Vitamins with possible coenzyme functions are B12 and vitamin A which acts as a cofactor in reactions enabling vision.