coenzyme

https://doi.org/10.1351/goldbook.C01126
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).
Source:
PAC, 1994, 66, 2587. 'Glossary of bioanalytical nomenclature - Part 1: General terminology, body fluids, enzymology, immunology (IUPAC Recommendations 1994)' on page 2593 (https://doi.org/10.1351/pac199466122587)