The tortuous road to the adoption of katal for the expression of catalytic activity by the General Conference on Weights and Measures.
BACKGROUND
The "unit" for "enzymic activity" (U = 1 micromol/min) was recommended by the International Union of Biochemistry and Molecular Biology (IUB) in 1961 and is widely used in medical laboratory reports. The general trend in metrology, however, is toward global standardization through defining units coherent with the International System of Units (SI).


METHODS
Several proposals were advanced from the IFCC, International Union of Pure and Applied Chemistry, and IUB regarding the definition for enzymic activity as well as the terms for kind-of-quantity, units, symbol, and dimension. In 1977, international agreement was reached between these bodies and WHO that "catalytic activity" (z), of a catalyst in a given system is defined by the rate of conversion in a measuring system (in mol/s) and expressed in "katal" (symbol, kat; equal to 1 mol/s). The katal is invariant of the measurement procedure, but the numerical quantity value is not. Gaining support for the katal from the final arbiter, the General Conference on Weights and Measures, was slow, but Resolution 12 of 1999 adopted the katal (symbol, kat) as a special name and symbol for the SI-derived unit, mol/s, used in measuring catalytic activity.


CONCLUSIONS
Laboratory results for amounts of catalysts, including enzymes, measured by their catalytic activity can now officially be expressed in katals and are traceable to the SI provided that the specified indicator reaction reflects first-order kinetics. The conversion from "unit" is: 1 U = 16.667 x 10(-9) kat. Further derived quantities have coherent units such as kat/L, kat/kg, and kat/kat = 1.
Dybkaer
René
R
Department of Standardization in Laboratory Medicine, H:S Frederiksberg Hospital, Copenhagen Hospital Corporation, Nordre Fasanvej 57, DK-2000 Frederiksberg, Denmark.
D002384:Catalysis; D004798:Enzymes / Q000266:history / Q000378:metabolism / Q000592:standards*; D049673:History, 20th Century; D049674:History, 21st Century; D007391:International Cooperation / Q000266:history; D012958:Societies, Scientific / Q000266:history; D014894:Weights and Measures / Q000266:history*
D004798:Enzymes