U or enzyme activity unit

A unit of enzyme activity adopted in 1964 by the International Union of Biochemistry,¹ having been defined by its Enzyme Commission in 1961.² One unit is the amount of enzyme activity which will catalyse the transformation of 1 micromole of the substrate per minute under standard conditions. The unit was not given a name. Symbol, U.

This unit was replaced in 1978 by the katal. 1 U corresponds to 16.67 nanokatals.

1.
International Union of Biochemistry.
Enzyme Nomenclature: Recommendations 1964 of the International Union of Biochemistry.
Amsterdam: Elsevier, 1965.

See Chapter 4.

2.
International Union of Biochemistry.
Report of the Commission on Enzymes.
Oxford: Pergamon Press, 1961.