The Ammonia and Methylamine Active Transport System of Aspergillus nidulans

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Abstract
Conidia of A. nidulans germinated on glutamate have a single system for the active transport of ammonia and methylamine against a concentration gradient. The transport of methylamine is inhibited by azide, N-ethylmaleimide, valinomycin and anaerobiosis; it has a pH optimum of about 6.3 and a temperature optimum of 40.degree. C. The affinity of the system for methylamine (Km 13 .mu.M) is about 20% of that for ammonia; the Vmax is also much lower. This transport system is present in methylamine-resistant mutants (meaA and meaB loci) and its formation is repressed in wild type and mutants by ammonia or a metabolite of ammonia. The system may function in the scavenging of low concentrations of ammonia during N starvation or during growth on other major N sources.

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