Three major reactions in all cells The Fate of Ammonium Three major reactions in all cells Carbamoyl-phosphate synthetase I two ATP required - one to activate bicarb, one to phosphorylate carbamate Glutamate dehydrogenase reductive amination of alpha-ketoglutarate to form glutamate Glutamine synthetase ATP-dependent amidation of gamma-carboxyl of glutamate to glutamine

Glutamine Synthetase A Case Study in Regulation GS in E. coli is regulated in three ways: Feedback inhibition Covalent modification (interconverts between inactive and active forms) Regulation of gene expression and protein synthesis control the amount of GS in cells But no such regulation occurs in eukaryotic versions of GS

Allosteric Regulation of Glutamine Synthetase Nine different feedback inhibitors: Gly, Ala, Ser, His, Trp, CTP, AMP, carbamoyl-P and glucosamine-6-P Gly, Ala, Ser are indicator of amino acid metabolism in cells Other six are end products of a biochemical pathway This effectively controls glutamine’s contributions to metabolism