ROLE OF GLUTAMINE SYNTHETASE, GLUTAMINE AND NH₄⁺ IN THE REGULATION OF GLUTAMINE UPTAKE IN THE CYANOBACTERIUM ANABAENA CYCADEAE

Abstract

The role of glutamine synthetase (GS), glutamine and/or NH₄⁺ in the regulation of glutamine uptake was studied in the cyanobacterium Anabaena cycadeae and its glutamine auxotrophic mutant lacking GS activity. The uptake pattern was found to be biphasic in both the strains consisting of an initial rapid phase lasting up to 60s followed by a slower second phase. The glutamine uptake was found to be maximum in glutamine medium whereas the cells incubated in N₂ and NO₃^- media showed similar uptake activities in both wild-type and mutant strain. The glutamine uptake system was found to be NH₄⁺-repressible. NH₄⁺ and glutamine did not inhibit the glutamine uptake in the glutamine auxotrophic mutant lacking GS activity, suggesting that NH₄⁺ and glutamine are not the repressor signals for glutamine uptake. The glutamine auxotrophic mutant also had higher level of glutamine uptake as compared to wild-type strain, indicating that GS activity is not necessarily involved in the uptake process of glutamine. Azaserine, an inhibitor of glutamate synthase (GOGAT), effectively inhibited the glutamine uptake in both the strains. Thus, it is suggested that the increased intracellular glutamine level regulates its own uptake in the cyanobacterium Anabaena cycadeae.