Inhibitory activity of sulfentrazone and its metabolic derivatives on soybean (Glycine max) protoporphyrinogen oxidase

The biological activities of sulfentrazone and its metabolic derivatives were investigated in an effort to elucidate the basis for soybean tolerance to this herbicide. All of the metabolic derivatives were less toxic than sulfentrazone as measured by electrolyte leakage from soybean leaf disks. Their in vivo activity correlated with the amount of protoporphyrin 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 (Protox) inhibition were 1.2, 0.35, 10, and 37 mu M for sulfentrazone and its 3-hydroxymethyl, 3-demethyl, and 3-carboxylic acid metabolic derivatives, respectively, and their binding affinities were related to their relative inhibitory potency. Oxidative degradation of sulfentrazone did not have a great influence on the overall shape of the molecule but affected the steric and electronic environment surrounding the methyl group on the triazolinone ring.