In Situ Regulation Studies of Escherichia coli Glutamine Synthetase

Abstract

The involvement of glutamine in the synthesis of purine and pyrimidine nucleotides, glucosamine 6-phosphate, and p -aminobenzoic acid, and in the formation of all the amino acids makes this metabolite a key intermediate in the synthesis of important end products such as proteins, nucleic acids, and complex polysaccharides. The enzyme of Escherichia coli and other gram-negative bacteria has been widely studied and appears to possess an extraordinary capability to integrate quite different metabolic signals and react appropriately. The E. coli glutamine synthetase (GS) is regulated at least by four different regulatory mechanisms, including repression of its synthesis, cumulative feedback inhibition by several end products of glutamine metabolism, modulation by the divalent metal ions, and covalent modification. With the aim of verifying in vivo the exceptional capability of GS to answer with an appropriate’ catalytic potency and regulatory susceptibility to different microenvironmental conditions, a method has been devised to study the GS cascade system in situ . E.coli can be made permeable to low molecular weight compounds while retaining GS and its cascade components by treating the cells with the nonionic detergent.