Enzyme unit

The enzyme unit, or international unit for enzyme (symbol U, sometimes also IU) is a unit of enzyme's catalytic activity. The enzyme unit, or international unit for enzyme (symbol U, sometimes also IU) is a unit of enzyme's catalytic activity. 1 U (μmol/min) is defined as the amount of the enzyme that catalyzes the conversion of one micromole of substrate per minute under the specified conditions of the assay method. The specified conditions will usually be the optimum conditions, which including but not limited to temperature, pH and substrate concentration, that yield the maximal substrate conversion rate for that particular enzyme. In some assay method, one usually takes a temperature of 25°C. The enzyme unit was adopted by the International Union of Biochemistry in 1964. Since the minute is not an SI base unit of time, the enzyme unit is discouraged in favor of the katal, the unit recommended by the General Conference on Weights and Measures in 1978 and officially adopted in 1999.