title: The role of specific cations in regulation of cyanobacterial glutamine synthetase.
abstract: Purified glutamine synthetase from the cyanobacterium Anabaena cylindrica required a divalent cation for activity. Maximum biosynthetic activity required Mg2+ (25 mM when supplied alone). Co2+ and Mn2+ each supported up to 20% of this activity; 12 other cations tested were ineffective. At 2.5 - 10 mM Mg2+, 0.1 mM Co2+ or ethylene glycol-bis-(beta-aminoethyl ether) N,N'-tetraacetic acid (EGTA) stimulated GS activity to maximum rates; other divalent cations (particularly Mn2+) inhibited Mg2+-dependent activity. At 5 mM Mg2+ the Kappm for NH+4 (0.05 mM) was 20-fold lower than at 25 mM Mg2+; added Co2+ did not markedly alter this low Km for NH+4; this could be physiologically important.
mesh_terms: D000641:Ammonia / Q000494:pharmacology; D002413:Cations, Divalent; D003035:Cobalt / Q000494:pharmacology; D000458:Cyanobacteria / Q000201:enzymology*; D005974:Glutamate-Ammonia Ligase / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology
chemical_list: D002413:Cations, Divalent; D003035:Cobalt; D008345:Manganese; D000641:Ammonia; D005974:Glutamate-Ammonia Ligase; D008274:Magnesium