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noun, plural: coenzymes

A complex organic (or metalloorganic) molecule required by a particular enzyme to carry out catalysis of a chemical reaction


Coenzymes are small organic molecules that are needed by certain enzymes for them to function. Coenzymes are nonprotein molecules although some are vitamins, particularly those that are phosphorylated derivaties of water-soluble vitamins. They participate in catalysis when they bind to the active site of the enzyme (called apoenzyme) and subsequently form the active enzyme (called holoenzyme). Although coenzymes activate enzymes they are not considered as substrates of the reaction.

The main function of the coenzyme during catalysis is to act as intermediate carriers of transferred electrons or functional groups in a reaction.

Examples of coenzymes are nicotineamideadenine dinucleotide (NAD), nicotineamide adenine dinucelotide phosphate (NADP), and flavin adenine dinucleotide (FAD). These three coenzymes are involved in oxidation or hydrogen transfer. Another is coenzyme A (CoA) that is involved in the transfer of acyl groups.


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