Abstract
Summary: The purification, location, properties and regulation of glutamine synthetase (GS) from the facultative methylotroph Hyphomicrobium X were investigated. The enzyme was purified to homogeneity by differential centrifugation, Blue Sepharose CL-6B chromatography and Sephadex G-25 gel filtration. The specific activity of the purified enzyme was 44.7 μmol min-1 (mg protein)-1. GS was cytoplasmic in location with no direct association with DNA, membranes or the enzyme glutamine: 2-oxoglutarate aminotransferase (GOGAT). The molecular mass of the native enzyme was 638 kDa; it was composed of 12 subunits of molecular mass 53 kDa. Double reciprocal plots showed that the enzyme followed Michaelis-Menten kinetics. The apparent K m values for hydroxamate and glutamine in the γ-glutamyl transferase assay were 7.0 and 5.0 mM respectively; those of ammonia, glutamate and ATP in the biosynthetic assay were 0.032, 31.1 and 0.37 mM respectively. GS activity was controlled by covalent modification, the presence of specific divalent cations and feedback inhibition by several end-products of glutamine metabolism.
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