Bioactivation of the mushroom hydrazine, agaritine, to intermediates that bind covalently to proteins and induce mutations in the Ames test

The present study was undertaken to establish whether liver and kidney enzyme systems, from rat and mouse, have the potential to metabolise and bioactivate agaritine, beta-N-(gamma-L(+)glutamyl)-4- (hydroxymethyl)phenylhydrazine, the most abundant hydrazine present in the edible mushroom Agaricus bisporus. Agaritine was weakly mutagenic, in the absence of an activation system, in Salmonella typhimurium strain TA104. Rat kidney homogenates, characterised by high gamma- glutamyl transpeptidase activity, enhanced the mutagenic response. In contrast, hepatic microsomes, having very low gamma-glutamyl transpeptidase activity, did not influence the mutagenicity of agaritine. However, hepatic microsomes could further potentiate the mutagenic response induced by the kidney. Agaritine was a good substrate for purified gamma-glutamyl transpeptidase, being converted to a major metabolite, 4-(hydroxymethyl)phenylhydrazine, formed as a result of the loss of the glutamyl moiety. Kidney homogenates from the rat and mouse also catalysed this reaction, the former being the more effective. Metabolism of agaritine was suppressed by serine-borate, an inhibitor of gamma-glutamyl transpeptidase. Kidney homogenates from rat and mouse could metabolise agaritine to intermediate(s) that bound covalently to proteins, with the rat preparations being the more effective; covalent binding was inhibited by glutathione. In contrast, hepatic preparations alone were ineffective in producing such covalent binding but did further increase the covalent binding mediated by the kidney preparations. It is concluded that rat and mouse kidney homogenates catalyse the removal of the glutamyl group from agaritine to yield the reactive free hydrazine, which is further converted to the highly reactive diazonium ion by hepatic microsomes.