The dissociable, low-relative-molecular-mass active group of an enzyme which transfers chemical groups, hydrogen or electrons. A coenzyme binds with its associated protein (apoenzyme) to form the active enzyme (holoenzyme).
PAC, 1994, 66, 2587 (Glossary of bioanalytical nomenclature - Part 1: General terminology, body fluids, enzymology, immunology (IUPAC Recommendations 1994)) on page 2593
See also:
PAC, 1992, 64, 143 (Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)) on page 150