Studies on glutamine synthetase. Purification of the enzyme from mung bean (Phaseolus aureus) seedlings and modulation of the enzyme-antibody reaction by the substrates.
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Date
1979-03
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Abstract
Glutamine synthetase (L-glutamate : ammonia ligase, EC 6.3.1.2)
from Phaseolus aureus (mung bean) seedlings was purified to homogeneity by
ammonium sulphate fractionation, DEAE-cellulose chromatography, Sephadex
G-200 gel filtration and affinity chromatography on histidine-Sepharose. The
enzyme had a molecular weight of 775,000 ± 25,000. The enzyme consisted of
identical subunits with an approximate subunit molecular weight of 50,000. Hyperbolic
saturation curves were obtained with the substrates, glutamate, ATP and
hydroxylamine.
Antibody, raised in the rabbit, against mung bean glutamine synthetase, completely
inhibited the activity of the enzyme. Preincubation of the enzyme with glutamate
and ATP, prior to the addition of the antibody, partially protected the enzyme
against inhibition. The Km values of this enzyme-antibody complex and the native
enzyme were identical (glutamate, 2.5mM; ATP, 1 mM; hydroxylamine, 0·5 mM).
The Km values of the partially inhibited enzyme (the enzyme pretreated with antibody
prior to the addition of substrates) were 2-fold higher than those of the native
enzyme. These results suggested that the substrate-induced conformational changes
in the enzyme were responsible for the protection against inhibition of the enzyme
activity by the antibody.
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Keywords
Mung bean, glutamine synthetase, antibody interactions, Phaseolus aureus
Citation
Seethalakshmi S, Rao N Appaji. Studies on glutamine synthetase. Purification of the enzyme from mung bean (Phaseolus aureus) seedlings and modulation of the enzyme-antibody reaction by the substrates. Journal of Biosciences. 1979 Mar; 1(1): 13-25.