(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 ]

n. [ Pref. en- (Gr. 'en in) + Gr. zy`mh leaven. ] (Physiol. Chem.) A protein produced by a living organism, capable of catalyzing a chemical reaction. Almost all processes in living organisms require some form of enzyme to cause the reactions to occur at a rate sufficient to support life. There are a very wide variety of enzymes, each specifically catalyzing a different chemical reaction, the sum of which cause the bulk of the physiological changes observed as life processes. Enzymes, like most proteins, are synthesized by the protein-synthetic mechanism of the living cell, at special sites on ribosomes, using the genetic information in messenger RNA transcribed from the genetic instructions stored as nuleotide sequences in the DNA (or in some viruses, the RNA) of the genome. Some examples of enzymes are: pepsin, diastase, rennet, DNA polymerase, invertase, glucose oxidase, protease, and ribonuclease. There are many other types of enzyme. [ 1913 Webster +PJC ]

The 1913 Webster defined an enzyme as:
An unorganized or unformed ferment, in distinction from an organized or living ferment; a soluble, or chemical, ferment. [ PJC ]

n. [ . ] (Bioch.) Any one of a class of proteins that are converted, in the normal course of cellular metabolism, into one or more active enzymes; also called zymogen. The conversion usually is due to a specific cleavage of a peptide bond by another enzyme, or may be due to acid. [ PJC ]