[14C]Methylamine was transported into mycelial cells of Stemphylium botryosum by a specific and energy-dependent transport system having an optimum at pH 6·0, a Km of 12·5 μm and a Vmax of 4·1 μmol (g dry wt)−1 min−1; uptake occurred against a concentration gradient. NH4+ competitively inhibited methylamine transport with higher affinity towards the latter system. Sucrose and nitrate were required during transport for maximal activity. Highest transport activity developed in nitrate-grown mycelium. Nitrogen starvation decreased the activity by approximately 60%. Preloading of mycelium with glutamine, asparagine or ammonia almost completely prevented methylamine uptake. Transport activity was inversely proportional to the intracellular concentration of the l-amides. It is postulated that ammonia uptake might be regulated by l-amides rather than by ammonia.
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