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.
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)
White Book, 2nd ed., p. 93 (https://www.qmul.ac.uk/bibliog/white.html)