Glutamine synthetase root nodules

Bennett, M.J. Cullimore, J.V. (1989). Glutamine synthetase isoenzymes of Phaseolus vulgaris L. subunit composition in developing root nodules and plumules. Planta 179, 433-40. 

Cai, X. Wong, P.P. (1989). Subunit composition of glutamine synthetase isoenzymes from root nodules of bean (Phaseolus vulgaris L.). Plant Physiology 91, 1056-62. 

Primary structure and differential expression of glutamine synthetase genes in nodules, roots and leaves of Phaseolus vulgaris. The EMBO Journal 5, 1429-35. 

Tingey, S.V., Walker, E.L. Coruzzi, G.M. (1987). Glutamine synthetase genes of pea encode distinct polypeptides which are differentially expressed in leaves, roots and nodules. The EMBO Journal 6, 1-9. 

Branjeon, J., Hirel, B. Forchioni, A. (1988). Immunogold localization of glutamine synthetase in soybean leaves, roots and nodules. Protoplasma 151, 88-97. 

Gebhardt, C., Olivier, J.E., Forde, B.G., Saarelainen, R. Miflin, B.J. (1986). Primary structure and differential expression of glutamine synthetase genes in nodules, roots and leaves of Phaseolus vulgaris. The EMBO Journal 5, 1429-35. 

Figure 9.41 Chromatograms of enzyme assay media. (A) Elution profile of the assay medium of glutamine synthetase. Alder root nodule enzyme plus assay mixture was incubated for IS minutes. (B) Elution profile of the assay medium of glutamate synthetase. Rice leaves enzyme plus assay mixture was incubated for 15 minutes. (From Martin et al., 1982.)...

The short-lived radionuclide, has been extremely useful in studies of N2 fixation and NH4 assimilation. Wolk and his collaborators have demonstrated that the glutamine synthetase/glutamate synthase pathway is the major assimilatory route for NH4 in N2-fixing cultures of Anabaena and many other cyanobacteria. They have extended these studies to show that the labeling pattern observed after exposure of detached or attached soybean root nodules to [ N]N2 was similar to that observed in Anabaena. On this basis Meeks et al. (19) concluded that the primary pathway for assimilating NH4" derived from N2 in soybean nodules involves the sequential assimilatory activities of glutamine synthetase and glutamate synthase. 

Wedler f al. (1978) have identified two forms of glutamine synthetase in Bacillus caldolytiens and Darrow and Knotts (1977) have shown two forms in Rhizobium japonicum and other free living root nodule bacteria. In both cases the two forms differ in their isoelectric points and stability. The work of Darrow and Knotts (1977) indicates that the two forms are not the result of differences in adenylation state of a single form. Type I appears similar to the E. coli enzyme in stability and in being susceptible to adenylation. Type II however is not adenylated and is more unstable. 

McFarland et al. (1976) have concluded from the molecular weights, subunit structure and electron micrographs of purified glutamine synthetase from soybean root nodule cytosol that the eight subunits of the enzyme are arranged in two sets of planar tetramers, 1 nm apart, forming a cubical configuration with dimensions of about 10 nm across each side. 

Nucleotides have also been shown to inhibit glutamine synthetase from other sources, notably ADP, 5 -AMP, and CTP inhibit the enzyme from soybean root nodules (McParland et al., 1976), 5 -AMP and CTP that from E. coli (Woolfolk and Stadtman, 1967), B. subtilis (Deuel and Stadtman, 1970), and N. crassa (Kapoor and Bray, 1968), and 5 -AMP and CMP inhibit the Chlorella enzyme (Evstigneeva, et al., 1974). In contrast the rat liver and ovine brain enzymes are not appreciably inhibited by these nucleotides (Meister, 1974). When testing for inhibition by nucleotides it is necessary to have sufficient divalent cation present to ensure that inhibition is not simply a result of inadequate divalent cations due to chelation by the nucleotide. The variation in inhibition by nucleotides is dependent to some degree on the source of divalent metal cation thus O Neal and Joy (1975) found ADP and 5 -AMP to be more inhibitory to the Mg +-compared with the Mn +-dependent activity. 5 -AMP was also found to be more inhibitory to the magnesium dependent activity of B. subtilis enzyme (Deuel and Stadtman, 1970). 

In the lupin root nodule (Scott ct al., 1976) AS activity rapidly increased 13 days after innoculation, in conjunction with nitrogenase and glutamine synthetase (see Robertson and Faraden, this volume. Chapter 2) and stayed constant for a further 10 days. 

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