A molecular species produced by living systems of biological origin when
it is composed of two parts of different origins, e.g. a conjugate of a
xenobiotic with some groups, e.g. glutathione, sulfate or glucuronic acid,
to make it soluble in water or compartmentalized within the cell.
Source:
PAC, 1997, 69, 1251
(Glossary of terms used in bioinorganic chemistry (IUPAC Recommendations 1997))
on page 1260