The ammonium transport system of Anabaena variabilis Kütz ATCC 29413 was studied with regard to its repression and derepression using [14C]‐methylammonium as an analogue for ammonium. Whereas N2‐grown cells showed an active ammonium transport system, the latter was repressed in ammonium‐grown cells. Repression of the ammonium transport system by ammonium did not require ammonium assimilation or de novo protein synthesis, suggesting that ammonium itself was the repressor signal. The derepression of the ammonium transport system however, required de novo protein synthesis and glutamine synthetase activity.
Methylammonium uptake and metabolism was studied in Nostoc sp. ANTH (a free-living cultured isolate from Anthoceros punctatus). Unlike other cyanobacteria, Nostoc sp. ANTH assimilated methylammonium as a fixed nitrogen source. While N2-grown Nostoc sp. ANTH cells showed ammonium transport characteristics similar to those in other cyanobacteria, a specific energy-dependent methylammonium transport was noticed in methylammonium-grown cells. Unlike methylammonium/ammonium transport in N2-grown cells, methylammonium transport in methylammonium-grown cells was neither affected by ammonium nor by L-methiOnhe-DLsulphoximine.
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