A Reappraisal of the γ-Glutamylcysteine Synthetase Activity in Haemolysates from Normal Erythrocytes by Two Different Methods

Abstract

γ-Glutamylcysteine synthetase catalyses the combination of l-glutamate and l-cysteine to form γ-glutamylcysteine with a stoichiometric conversion of ATP to ADP and inorganic phosphate (P_i). During the estimation of this enzyme in haemolysates from normal erythrocytes it was found that the P_i released was more than the amount of γ-glutamylcysteine synthesised. Furthermore, the activity estimated by analysing either product was higher than the corresponding values reported in the literature. An investigation into these discrepancies resulted in improvements of the assay methods which produced two substantially different normal ranges for the γ-glutamylcysteine synthetase activity in haemolysates: one derived from the P_i released and the other from the γ-glutamylcysteine synthesised during the enzymatic reaction.

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