03114 IUPAC Gold Book - international unit 10.1351/goldbook.I03114 I03114 current 1 The unit of enzyme activity proposed by the International Union of Biochemistry in 1964. Specifically, it is the amount of enzyme that catalyses the conversion of one micromole of substrate per minute under the specified conditions of the assay method. This unit is no longer recommended because the term does not indicate what physical quantity it refers to, and because the minute is not the SI unit of time. assay https://goldbook.iupac.org/terms/view/A00470 enzyme activity https://goldbook.iupac.org/terms/view/E02154 PAC, 1994, 66, 2587. 'Glossary of bioanalytical nomenclature - Part 1: General terminology, body fluids, enzymology, immunology (IUPAC Recommendations 1994)' on page 2593 (https://doi.org/10.1351/pac199466122587) https://goldbook.iupac.org/terms/view/I03114/html https://goldbook.iupac.org/terms/view/I03114/json https://goldbook.iupac.org/terms/view/I03114/plain Citation: 'international unit' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.I03114 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-05-14T19:46:28+00:00