The distinction between γ-glutamylhydroxamate synthetase and l -glutamine–hydroxylamine glutamyltransferase activities in rat tissues. Studies in vivo

The formation of γ-glutamylhydroxamate by homogenates under optimum assay condition showed an inconstancy in the ratios of the enzyme activities utilizing l-glutamate and ATP (γ-glutamylhydroxamate synthetase) and l-glutamine and ADP (l-glutamine–hydroxylamine glutamyltransferase) in a number of normal and neoplastic rat tissues. Although γ-glutamylhydroxamate synthetase activities in adult livers and kidneys were identical in males and females, l-glutamine–hydroxylamine glutamyltransferase activities in the organs of females were significantly lower. The developmental formations of the two activities in liver, kidney, brain and muscle were not simultaneous. The l-glutamine–hydroxylamine glutamyltransferase activity in foetal liver or neonatal kidney could be prematurely evoked by thyroxine, but the γ-glutamylhydroxamate synthetase activity remained unchanged. Injections of cortisol also had dissimilar effects on the two activities in thymus and hepatomas. The discrepant tissue distribution, asynchronous developmental formation and differential response to several hormonal stimuli provide evidence in vivo that the two activities are not catalysed by the same protein.