Activated Glutamate Intermediate in the Enzymatic Synthesis of Glutamine

Inhibition of glutamine synthetase by methionine sulfoximine. Studies On Methionine sulfoximine phosphate

“…The present studies on the inhibition of glutamine synthetase by methionine sulfoximine and methionine sulfoximine phosphate have developed from earlier work in this laboratory on the unusual specificity of this enzyme; however, additional work is needed in order to fully integrate the present studies with the earlier ones. Previous studies have shown that both l-and -glutamate are good substrates for the synthesis of the corresponding isomers of glutamine and -glutamyl hydroxamate (Levintow and Meister, 1953;Meister, 1968) and of pyrrolidonecarboxylate (Krishnaswamy et al, 1960(Krishnaswamy et al, , 1962. On the other hand, only the l isomer of glutamine is significantly active in the -glutamyl transfer and arsenolysis reactions catalyzed by sheep brain glutamine synthetase (Meister, 1962;Wellner, 1963); in addition, there is evidence that the enzyme binds D-glutamine very much less effectively than L-glutamine (Krishnaswamy et al, 1962).…”

Design, Synthesis, and Activity of Analogues of Phosphinothricin as Inhibitors of Glutamine Synthetase

“…It catalyses the first step in nitrogen assimilation, the ATP-dependent formation of glutamine from glutamate and ammonia. , The amide group is then transferred by a glutamate synthase (GOGAT) to α-ketoglutarate, yielding two glutamate molecules. The former closes the so-called GS−GOGAT cycle, the latter works in turn as a nitrogen donor in the biosynthesis of numerous biologically important compounds, including amino acids, purines, pyrimidines, and glucosamine. , GS-catalyzed reaction involves the initial synthesis of activated γ-glutamyl phosphate, followed by replacement of the phosphate group by ammonia with the formation of a phosphorylated tetrahedral intermediate . X-ray analysis showed that bacterial GS is a homododecamer built of two hexameric rings of subunits, with 12 “bifunnel”-shaped active sites formed between monomers, where ATP and glutamate bind at opposite ends .…”

Exploring the Catalytic Mechanism of Human Glutamine Synthetase by Computer Simulations

“…Initial biochemical and enzymological studies characterized the reaction catalyzed by GS, suggesting the two-step model for glutamine biosynthesis accepted today, that implies the initial formation of the activated intermediate γ-glutamyl phosphate (γ-Glu-P), followed by the nucleophilic attack of ammonia on that intermediate, releasing phosphate and yielding glutamine. ,− Crystal structures of different enzyme–substrate complexes led to the proposal of a structural model for the reaction mechanism of GSI, defining the role of several active site amino acids in catalysis . However, to date, there are no accurate studies related to the active site structural features that are the molecular determinants of catalytic activity, especially for type II GS.…”