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Updated: Aug 8, 2026

Spectrophotometric Screening for Potential Inhibitors of Cytosolic Glutathione S-Transferases
Published on: October 10, 2020
Inhibition of Glutamine Synthetase from Pea by Tabtoxinine-beta-lactam
M D Thomas1, P J Langston-Unkefer, T F Uchytil
1Department of Plant Pathology, University of Wisconsin-Madison and United States Department of Agriculture, Agricultural Research Service.
Abstract:
Tabtoxinine-beta-lactam, a hydrolytic product of tabtoxin produced by Pseudomonas syringae pv. tabaci, apparently inactivates pea seed glutamine synthetase. Inhibition of the enzyme's initial velocity is linear over a range of 0.5 to 5 millimolar tabtoxinine-beta-lactam in the presence of 10 millimolar glutamate. A method for the purification of glutamine synthetase from dried peas is presented which gives a 30% yield with a 2,000-fold increase in specific activity. A method for obtaining highly purified tabtoxinine-beta-lactam and tabtoxin in good yields is also presented. The authenticity and purity of tabtoxinine-beta-lactam and tabtoxin were verified by chromatography, biological activity, and (1)H and (13)C nuclear magnetic resonance spectroscopy.
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