Regulation of glutamine uptake in the cyanobiont Nostoc ANTH

Abstract Glutamine uptake in the cyanobiont Nostoc ANTH was energy-dependent and repressed in ammonia-grown cells. l -Methionine- dl -sulphoximine (MSX), a glutamate analogue and an inhibitor of glutamine synthetase (GS), did not affect glutamine uptake whereas azaserine, an inhibitor of glutamate synthase (GOGAT) did, suggesting that GS activity is not necessarily involved in the glutamine uptake system and that increased intracellular glutamine level regulates its own uptake. Repression of glutamine uptake by ammonia did not require de novo protein synthesis but required GS activity, suggesting that ammonia itself was not the repressor signal. The derepression of the glutamine uptake system did not require GS activity but required de novo protein synthesis.