Abstract
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 activity.