Mg2+ is bound to glutamine synthetase extracted from bovine or ovine brain in the presence of L-methionine-S-sulfoximine phosphate.
Purified glutamine synthetase from bovine or ovine brain had no tightly bound Mn2+. By extraction of bovine or ovine brain glutamine synthetase in the presence of L-Met-S-sulfoximine phosphate and ADP in metal ion-free water and 0.1 M KCl, only endogenously bound divalent cations were trapped on the enzyme. Enzyme complexes isolated by immunoprecipitation contained less than 0.05 Mn2+ and 1.5 +/- 0.2 Mg2+ per subunit. Without inactive complex formation, the enzyme immunoprecipitated from extracts contained undetectable Mn2+ (less than 0.01 eq per subunit) and 0.1-2.0 eq of Mg2+ per subunit. Direct binding measurements showed that the purified bovine brain enzyme contained two divalent cations bound at the active site of each subunit. Thus, although either Mg2+ or Mn2+ supports enzyme activity in vitro, Mg2+ rather than Mn2+ appears to be bound to brain glutamine synthetase in vivo.
Maurizi
M R
MR
Pinkofsky
H B
HB
McFarland
P J
PJ
Ginsburg
A
A
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D001667:Binding, Competitive; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D004591:Electrophoresis, Polyacrylamide Gel; D005974:Glutamate-Ammonia Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D008274:Magnesium / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism; D008717:Methionine Sulfoximine / Q000494:pharmacology*; D012756:Sheep
D008717:Methionine Sulfoximine; D008345:Manganese; D000255:Adenosine Triphosphate; D005974:Glutamate-Ammonia Ligase; D008274:Magnesium