One of a group of related enzymes catalysing the same reaction but having different molecular structures and characterized by varying physical, biochemical and immunological properties.
Sources:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 158 (https://doi.org/10.1351/pac199264010143)
PAC, 1994, 66, 2587. 'Glossary of bioanalytical nomenclature - Part 1: General terminology, body fluids, enzymology, immunology (IUPAC Recommendations 1994)' on page 2594 (https://doi.org/10.1351/pac199466122587)
See also:
White Book, 2nd ed., p. 93 (https://iupac.qmul.ac.uk/bibliog/white.html)