(Biochem.) a molecule that is essential for the activity of some enzymes; it may exist free in solution within a living organism, but functions by binding to an enzyme to assist in catalyzing a reaction. The molecule itself may be temporarily changed during the reaction, but is ultimately restored to its original form. Many vitamins function as coenzymes. [ PJC ]

(Biochem.) a coenzyme (C21H36N7O16P3S) that participates in the transfer of acetyl groups in biochemical reactions; -- abbreviated CoA. It contains adenosine, phosphate, pantothenic acid and cysteamine groups. The acetyl group to be transferred during biosynthesis is temporarily attached to the free sulhydryl of the cysteamine group to form a thioester, in which state it is called acetyl coenzyme A. The strength of a preparation of coenzyme A may be expressed by the Lippman unit; one milligram of CoA contains 413 Lippman units. [ PJC ]