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Studies on Cyanobacterial Glutamine Synthetase

出版	University of Dundee, Agosto, 1979
URL	http://books.google.com.hk/books?id=256rXwAACAAJ&hl=&source=gbs_api

註釋Glutamine synthetase has been purified to homogeneity from three cyanobacteria: Anabaena cylindrica, a species of Nostoc (isolated from the lichen Peltigera canina) and Plectonema boryanum. The activities of the A. cylindrica, Nostoc sp and P. boryanum enzymes in the biosynthetic assay were, respectively, 9.4, 6.5 and 5.0 umol product formed. mg protein -1.min-1. Stabilization of the enzyme required Mg2+, glutamate, EDTA and a thiol reagent to be present during purification. The molecular weight of the A. cylindrica enzyme was 591,000 as estimated by sedimentation analysis, 660,000 by gel filtration and 565,000 by polyacrylamide gel electrophoresis; the Nostoc sp and P. boryanum enzymes gave values in the same region. The molecular weights of the sub-units ofeach enzyme were approximately 50,000. Electron microscopy revealed that each molecule was composed of 12 sub-units arranged in two superimposed hexagonal rings. When dialysed in the absence of stabilizing ligands the A. cylindrica enzyme lost activity and the protein band characteristic of the native enzyme was replaced by three bands with approximate molecular weights of 510,000, 310,000, and 130,000. These sub-species re-associated and activity was restored by adding 2-mercaptoethanol and substrates. The Nostoc sp and P. boryanum enzymes did not show such deactivation. Some kinetic and regulatory properties of the purified A. cylindrica, Nostoc and P. boryanum glutamine synthetases were determined. The feed-back inhibition pattern observed with ...