Mode of Action of the Toxin from Pseudomonas phaseolicola | Zendy

Leslie Q. Tam | Zendy; Suresh S. Patil | Zendy

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Mode of Action of the Toxin from Pseudomonas phaseolicola

Author(s) -

Leslie Q. Tam,

Suresh S. Patil

Publication year - 1972

Publication title -

plant physiology

Language(s) - English

Resource type - Journals

SCImago Journal Rank - 3.554

H-Index - 312

eISSN - 1532-2548

pISSN - 0032-0889

DOI - 10.1104/pp.49.5.808

Subject(s) - uncompetitive inhibitor , allosteric regulation , non competitive inhibition , michaelis–menten kinetics , chemistry , arsenate , ornithine , toxin , mixed inhibition , mode of action , kinetics , biochemistry , nuclear chemistry , enzyme , stereochemistry , enzyme assay , arginine , arsenic , organic chemistry , physics , amino acid , quantum mechanics

A chlorosis-inducing toxin of Pseudomonas phaseolicola was examined for inhibition of ornithine carbamoyltransferease prepared from acetone powder of bean (Phaseolus vulgaris L.) plants. The enzyme has a pH optimum at 8.5, involves a ternary complex reaction mechanism, and shows Michaelis constants of 5.0 mm and 1.7 mm for ornithine and carbamoylphosphate, respectively. Assuming reversible catalysis, Michaelas constants of 11 mm and 3.3 mm are calculated for citrulline and arsenate. Toxin induces allosteric competitive inhibition in relation to carbamoylphosphate and a noncompetitive mode of inhibition in relation to ornithine, except at high toxin concentrations where uncompetitive inhibition is observed. In the backward assay, competitive inhibition is observed for both arsenate and citrulline. Inhibition is increased with preincubation time and shows saturation kinetics with regard to toxin concentration.

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