Characterization of glutamine-synthetase from Beta vulgaris [fodder beets, pH optimum, nitrogen metabolism]
1981
Nesselhut, T. | Harnischfeger, G. (Goettingen Univ, (Germany, F.R.). Lehrstuhl fuer Biochemie der Pflanze)
Glutamine-synthetase (GS) from Beta vulgaris seedlings, purified 150-fold, was characterized with regard to its physiological substrate NH(,3). The data were compared to the unphysiological substrate NH(,2)-OH frequently used in the assay (both synthetase and transferase reaction). The pH-optimum was found at pH 7.5 for the synthetase and at pH 6.3 for the transferase reaction. Through plots of pKm vs pH, the pKe values for dissociable groups in the reaction center were found to be in the range from pH 7-8. Mg('2+)-ion serves as an allosteric effector with a Hill coefficient of 4.2. The results are discussed in relation to the control of nitrogen metabolism in Beta.
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