Bacterial glutamine synthetase

Many enzymes (see Chapters 14 to 16) derive at least some of their catalytic power from oligomeric associations of monomer subunits. This can happen in several ways. The monomer may not constitute a complete enzyme active site. Formation of the oligomer may bring ail the necessary catalytic groups together to form an active enzyme. For example, the active sites of bacterial glutamine synthetase are formed from pairs of adjacent subunits. The dissociated monomers are inactive. 

Covalent interconversion of enzymes is well established as a fundamental theme in metabolic regulation. The prototypic reversible interconverting systems include the sequence of phosphorylation/dephosphorylation steps in the activation of mammalian glycogen phosphorylase and pyruvate dehydrogenase as well as the nucleotidyla-tion/denucleotidylation using UTP and ATP in the bacterial glutamine synthetase cascade (see Fig. 1.). 

Bacterial glutamine synthetase is feedback inhibited by serine, glycine, and alanine. Explain specifically the connection between these amino acids and glutamine that would account for the logic of this inhibition. 

RL Levine, CN Oliver, RH Fulks, ER Stadtman. Turnover of bacterial glutamine synthetase oxidative inactivation precedes proteolysis. Proc Natl Acad Sci (USA) 78 2120-2124, 1981. 

Bacterial glutamine synthetase is a huge enzyme which consists of 12 subunits forming two hexameric rings positioned face-to-face.89 90 There are 12 active... 

Moss J, Stanley SJ, Levine RL (1990) Inactivation of bacterial glutamine synthetase by ADP-ribosylation. In J. Biol. Cbem. 265 21056-21060. 

Tachiki et al. reported the production of theanine from glutamate and ethyl-amine through the coupling of baker s yeast preparations and bacterial glutamine synthetase. Because of the low reactivity of glutamine synthetase with ethylamine and the difficulty in pH control of the reaction mixture, the yield was not satisfatory. The production of theanine with cultured cells of Camellia sinensis has been performed, but it took a 4-week cultivation period. 

Tachiki, T., Suzuki, H., Wakisaka, S., Yano, T., and Tochikura, T. 1986. Production of y-glutamylmethylamide and y-glutamylethylamide by coupling of baker s yeast preparations and bacterial glutamine synthetase. J. Gen. Appl. Microbiol. 32 545 8. 

Wakisaka, S., Y. Ohshima, M. Ogawa, T. Tochikura, andT. Tachiki. 1988. Characteristics and efficiency of glutamine production by coupling of a bacterial glutamine synthetase reaction with the alcoholic fermentation system of baker s yeast. Appl. Environ. Microbiol. 64 2953-2957. 

Consider three forms of bacterial glutamine synthetase GS, the deadenylylated form GS-(AMP)i, a form with one AMP unit per 12 subunits and GS-(AMP)i2, the fully adenylylated form. 

Interpretation of bacterial glutamine synthetase is further complicated due to the enzyme existing in both adenylated and deadenylated forms. Whereas only the deadenylated form is biosynthetically active both forms catalyze transferase activity. Glutamine synthetase can also catalyze the arsenolysis of glutamine [Eq. (4)]. When the enzyme is incubated with L-glutamine, catalytic amounts of nucleotide and divalent metal ions, glutamine is converted to glutamate and ammonia. 

Kamnev A A, Antonyuk LP et al (2003) Application of emission Mossbauer spectroscopy to the study of cobalt coordination in the active centers of bacterial glutamine synthetase. Dokl Biochem Biophys 393 321-325... 

This enzyme [EC 2.7.7.42], also known as glutamateiam-monia-ligase adenylyltransferase, plays a key role in controlling bacterial nitrogen metabolism by controlling the state of adenylylation of glutamine synthetase. 

The mechanism of action of glutamine synthetase has been extensively studied, and both the bacterial and mammalian enzymes were reviewed in Volume X of this series (83, 84). Many experimental approaches have been applied to the question of the chemical activation of the y-carboxyl group of glutamate and its reaction with ammonia. All of these experiments supported the stepwise chemical mechanism outlined in reactions (24a) and (24b) (8J),... 

Unlike most known BLAs, which affect bacterial cell wall synthesis, 28 irreversibly inhibits glutamine synthetase, thus rendering the cell incapable of reassimilating the ammonia released by normal photorespiration. Toxic concentrations of... 

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