cofactors

https://doi.org/10.1351/goldbook.C01128
Organic molecules (cf. @C01126@) or ions (usually metal ions) that are required by an @E02159@ of its activity. They may be attached either loosely or tightly @P04893@) to the enzyme. A cofactor binds with its associated protein (apoenzymes), which is functionally inactive, to form the active enzyme (@H02836@).
Source:
PAC, 1992, 64, 143. (Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)) on page 150 [Terms] [Paper]