INHIBITORY ACTIVITY OF SULFENTRAZONE AND ITS METABOLIC DERIVATIVES ONSOYBEAN (GLYCINE-MAX) PROTOPORPHYRINOGEN OXIDASE

The biological activities of sulfentrazone and its metabolic derivativ es were investigated in an effort to elucidate the basis for soybean t olerance to this herbicide. All of the metabolic derivatives were less toxic than sulfentrazone as measured by electrolyte leakage from soyb ean leaf disks. Their in vivo activity correlated with the amount of p rotoporphyrin IX (Proto) accumulating in herbicide-treated tissues (i. e., more Proto accumulated in tissues treated with sulfentrazone than with the metabolites). I-50 values for protoporphyrinogen oxidase (Pro tox) inhibition were 1.2, 0.35, 10, and 37 mu M for sulfentrazone and its 3-hydroxymethyl, 3-demethyl, and 3-carboxylic acid metabolic deriv atives, respectively, and their binding affinities were related to the ir relative inhibitory potency. Oxidative degradation of sulfentrazone did not have a great influence on the overall shape of the molecule b ut affected the steric and electronic environment surrounding the meth yl group on the triazolinone ring.