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Metabolism of metolachlor by a microsomal fraction isolated from grain sorghum (Sorghum bicolor) shoots.

Authors
  • Moreland, D E
  • Corbin, F T
  • Novitzky, W P
  • Parker, C E
  • Tomer, K B
Type
Published Article
Journal
Zeitschrift für Naturforschung. C, Journal of biosciences
Publication Date
May 01, 1990
Volume
45
Issue
5
Pages
558–564
Identifiers
PMID: 2378670
Source
Medline
License
Unknown

Abstract

A microsomal fraction isolated from the shoots of 3- to 4-day-old, dark-grown, grain sorghum (Sorghum bicolor cv. Funk G 522 DR) seedlings was characterized. The preparations had a cytochrome P-450 content that varied from approximately 90 to 150 pmol P-450/mg protein with cytochrome P-420 varying from 0 to 3% of the P-450 content. Type I difference spectra were formed with cinnamic acid and metolachlor, and a type II spectrum was formed with tetcyclacis. In short-term assays with [14C]metolachlor as substrate, the preparations produced a single time-dependent product that separated on silica gel TLC plates developed in benzene/acetone (2:1, v/v). RF values for metolachlor and the metabolite were approximately 0.70 and 0.48, respectively. The microsomal reaction required NADPH and oxygen, and was inhibited by carbon monoxide, with the inhibition being partially reversed by actinic light. Compounds known to inhibit the activity of cytochrome P-450 monooxygenases (piperonyl butoxide, tetcyclacis, and tridiphane) also prevented formation of the metabolite. Identity of the metabolite was confirmed by TLC and positive ion thermospray LC/MS to be 2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-hydroxy-1-methylethyl)acetamide . Hence, the reaction catalyzed by the sorghum microsomes involved O-demethylation of the methoxypropyl side chain of metolachlor.

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