Glutamine synthase regulation

Even more important in the regulation of E. coli glutamine synthase activity is the reversible ATP-dependent adenylylation of a specific tyrosyl residue on each subunit. As the enzyme becomes progressively more adenylylated (up to the fully adenylylated form which contains 12 AMP groups per enzyme molecule), the enzyme becomes progressively less active. 

The glutamine synthase regulatory system has another important function. Protein Pll stimulates the dephosphorylation of the enhancer-binding transcriptional regulator NRI-P (NtrC-P). This slows transcription of the glutamine S5mthase gene (see Fig. 

Since biosynthesis of IMP consumes glycine, glutamine, tetrahydrofolate derivatives, aspartate, and ATP, it is advantageous to regulate purine biosynthesis. The major determinant of the rate of de novo purine nucleotide biosynthesis is the concentration of PRPP, whose pool size depends on its rates of synthesis, utilization, and degradation. The rate of PRPP synthesis depends on the availabihty of ribose 5-phosphate and on the activity of PRPP synthase, an enzyme sensitive to feedback inhibition by AMP, ADP, GMP, and GDP. 

Y. Hayashi, Y. Sawa, N. Fukuyama, H. Nakazawa, H. Matsuda, Preoperative glutamine administration induces heat-shock protein 70 expression and attenuates cardiopulmonary bypass-induced inflammatory response by regulating nitric oxide synthase activity, Circulation 106, 2601-07 (2002). 

Nitrogen and carbon regulation of glutamine synthetase and glutamate synthase in Corynebacterium glutamicum AXCC 13032. FEMS Microbiol. Lett., 205, 361-367. 

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