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.
PAC, 1997, 69, 1251. 'Glossary of terms used in bioinorganic chemistry (IUPAC Recommendations 1997)' on page 1260 (https://doi.org/10.1351/pac199769061251)