Glutamine synthetase deadenylylating enzyme

Abstract

The glutamine synthetase of Escherichia coli exists in various forms differing from each other by their content of covalently bound adenylyl groups ( Shapiro et al. , 1967 ; Wulff et al. , 1967 ). The biosynthetic activity of unadenylylated glutamine synthetase is very much greater with Mg 2+ as the activating cation than with Mn 2+, and its γ-glutamyl-transferase activity is insensitive to inhibition by many end product effectors ( Kingdon et al. , 1967 ). The biosynthetic activity of the adenylylated enzyme is relatively specific for Mn 2+, and its transferase activity is much more susceptible to feedback inhibition. An enzyme (ATP:glutamine synthetase adenylyltransferase) derived from E. coli catalyzes the covalent attachment of the AMP moiety of ATP to glutamine synthetase in a Mg 2+ dependent reaction that is stimulated by glutamine and inhibited by glutamate ( Kingdon et al. , 1967 ; Wulff et al. , 1967 ). The conditions of growth of E. coli determine the extent of adenylylation of the enzyme ( Kingdon and Stadtman, 1967). Kingdon and Stadtman (1967) and Heilmeyer et al. (1967) found evidence for in vivo deadenylylation of glutamine synthetase. The present communication describes some properties of an enzyme in soluble extracts of E. coli that catalyses the release of covalently bound 14C-AMP from glutamine synthetase; it is markedly stimulated by a-ketoglutarate and inhibited by glutamine. The significance of this activity in the control of glutamine synthetase activity and nitrogen metabolism in E. coli is discussed.