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Abstract
Conidia of Aspergillus 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°C. The affinity of the system for methylamine (K m 13 μ m) is about 20% of that for ammonia; the V max 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. It is proposed that the system functions in the scavenging of low concentrations of ammonia during nitrogen starvation or during growth on other major nitrogen sources.
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