N-15-NMR STUDY OF AMMONIUM ASSIMILATION IN AGARICUS-BISPORUS

Ammonium assimilation was studied by feeding [N-15]ammonium to activel y growing mycelium of Agaricus bisporus. Products of ammonium assimila tion were analysed using N-15-NMR. Participation of glutamine syntheta se, glutamate synthase and NADP-dependent glutamate dehydrogenase was determined by inhibiting glutamine synthetase with phosphinothricin an d glutamate synthase with azaserine. Our results clearly indicate that , under the conditions used, ammonium assimilation is mainly catalysed by the enzymes of the glutamine synthetase/glutamate synthase pathway . No indications were found for participation of NADP-dependent glutam ate dehydrogenase. Furthermore, N-15-labelling shows that transaminati on of glutamate with pyruvate to yield alanine is a major route in nit rogen metabolism Another major route is the formation of N-acetylgluco samine. Compared to the formation of N-acetylglucosamine there was onl y a limited formation of arginine.