Abstract
This chapter discusses the assay, purification, and properties of glutamine synthetase adenylyltransferase. Glutamine synthetase is adenylylated upon incubation with adenosine triphosphate (ATP): glutamine synthetase adenylyltransferase (adenylylating enzyme), ATP, Mg 2+ , and glutamine. The adenylylation of glutamine synthetase is paralleled by a decrease of its biosynthetic activity. The extent of this inactivation is used to determine the activity of the adenylylating enzyme. Apart from the biosynthesis of glutamine, glutamine synthetase catalyzes the transfer of the γ -glutamyl moiety of glutamine to hydroxylamine. This transfer activity (measured in the presence of adenosine diphosphate (ADP)) is not substantially affected by adenylylation. At a protein concentration of 10 mg/ml, the final preparation loses half of its activity in about four weeks upon storage at 4°. Maximal activity of the enzyme is observed at about pH 7.6 either in imidazole-HCl or Tris-HCl buffers. Concentrations of ATP higher than 1 m M inhibit the enzyme.
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