Production of ammonium dependent on basicL-amino acids byAnacystic nidulans

Abstract

The incubation of the cyanobacteriumAnacystis nidulans withL-Arg,L-Lys orL-Orn, but neither with the correspondingD-isomers nor with other twentyL-amino acids, resulted in the production of large amounts of ammonium which accumulated in the outer medium. Relevant properties of thisin vivo ammonium production activity have been studied in cell suspensions treated with the glutamine synthetase inactivatorL-methionine-D,l-sulfoximine (MSX) to prevent assimilation by the cells of the resulting ammonium. In addition to its specificity for the basicL-amino acids, the system exhibited a set of properties (K _m value for substrates, requirement of oxygen which is taken up stoichiometrically with the production of ammonium, inhibition by o-phenanthroline and divalent cations) all of which are shared by a peculiarL-amino acid oxidase recently isolated fromA. nidulans. The data strongly suggest the participation of this enzyme in the production of ammonium from basic amino acids byA. nidulans, an activity that could account for the ability of this cyanobacterium to use arginine as a nitrogen source.