EDTA effect on creatine kinase (CK) and on the SCE reagent.

The inclusion of EDTA in the creatine kinase reagent recommended by the Scandinavian Committee on Enzymes was shown to increase reagent stability from less than 24 h to 5 days. Part of this effect can be explained by the fact that EDTA delays the formation of inhibitory products formed when N-acetyl cysteine is oxidized. The addition of EDTA to the reagent also results in increased measured CK activity. This effect is more pronounced for CK-BB than for CK-MM. Calcium and ferric ions are shown to inhibit the enzyme and the chelation of these ions can partly explain the observed increase of CK acitivity.