3. 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

7. 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

9. 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