Assay for glutamine synthetase activity (Short Communication)

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Abstract
The use of phosphoenolpyruvate plus pyruvate kinase as an ATP-generating system in the assay for glutamine synthetase activity via the formation of γ-glutamylhydroxamate from glutamate and hydroxylamine with crude tissue preparations is shown to give values far in excess of the true glutamine synthetase activity of the tissue. This is due to the generation of pyruvate, which reacts with hydroxylamine to give a compound that is chromogenic with the ferric chloride reagent used for measuring γ-glutamylhydroxamate.