Chick brain glutamine synthetase and Mn2+-Mg2+ interactions.
Glutamine synthetase (GS) from the chick brain was purified to apparent homogeneity by ammonium sulfate fractionation followed by affinity chromatography, electrofocusing and Sephadex G-150 chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate analysis in polyacrylamide gel. By sedimentation equilibrium analysis and gel electrophoresis analysis, it was shown that the enzyme has a subunit molecular weight of 45,000 and a native molecular weight of 364,000, which is consistent with an octameric structure. Sedimentation analysis in the presence of Mg2+ revealed three different forms of macromolecules corresponding respectively to a monomer, a tetramer and an octamer. Among eight cations tested (Ca2+, Co2+, Fe2+, Li+, Mg2+, Mn2+, Ni2+, Zn2+) only Co2+, Mg2+ and Mn2+ supported GS activity; the order of activatory ability was Mg2+ greater than Co2+ greater than Mn2+. The maximum activating effect of Mn2+ occurs only within a very narrow range of concentration: with an excess of cation causing strong inhibition of GS activity. For each cation, maximal GS activity occurs at a defined cation/ATP ratio. A regulatory system in which Mn2+, modulates the Mg2+ dependent GS activity, is proposed; such cation interactions may be of significance in the intracellular control of glutamine synthesis.
D000818:Animals; D001921:Brain / Q000201:enzymology*; D001923:Brain Chemistry; D002645:Chickens; D002846:Chromatography, Affinity; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005974:Glutamate-Ammonia Ligase / Q000032:analysis / Q000302:isolation & purification / Q000378:metabolism*; D007525:Isoelectric Focusing; D008274:Magnesium / Q000502:physiology*; D008345:Manganese / Q000502:physiology*; D008970:Molecular Weight
D008345:Manganese; D005974:Glutamate-Ammonia Ligase; D008274:Magnesium