Glutamine synthetase of Bacillus stearothermophilus. Regulation, site interactions, and functional information

Biochemistry
F C WedlerA E Ashour

Abstract

The action of various feedback modifiers on Bacillus stearothermophilus glutamine synthetase has been investigated by initial velocity kinetics, using the Mn2+-stimulated biosynthetic assay at 55 degrees C. The most potent inhibitors, used singly, are AMP, L-glutamine, and L-alanine. Other modifiers of significance include glycine, CTP, L-histidine, glucosamine 6-phosphate, and GDP. Marked synergism of action is observed for AMP in the presence of L-glutamine, L-histidine, ADP, or glucosamine 6-phosphate (glucosamine-6-P), and for CTP with ADP or GDP. Inhibition by saturating levels of many modifiers is either less than 100%, or is not overcome by elevated substrate levels, or both. This argues for modifier binding sites separate from substrate sites, notably in the cases of AMP, L-glutamine, glycine, L-alanine, glucosamine-6-P, and CTP. Glycine and L-alanine are Vmax inhibitors, whereas L-glutamine, glucosamine-6-P, GDP, and CTP alter the binding of L-glutamate. ADP and L-histidine apparently can compete directly with MnATP, but AMP alters Mn-ATP binding from a separate site. The action of several modifiers requires or is enhanced by bound substrates. Considerable antagonistic interaction is observed in experiments with modifi...Continue Reading

Citations

Sep 1, 1995·Current Microbiology·C Palaniappan, M Gunasekaran
Jun 13, 1980·Biochimica Et Biophysica Acta·R Tuli, J Thomas
Mar 15, 1978·Biochemical and Biophysical Research Communications·F C WedlerJ Carfi

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