Studies on the fungitoxicity of captan

SUMMARY The cellular distribution of 35S after incubating labelled captan with Neurospora crassa conidia has been determined. Nearly all the 35S in the spores is bound to the water‐soluble and protein fractions. Thin‐layer chromatography of the hot‐water extract of spores has shown that 35S occurs largely in oxidized glutathione (GSSG) and in a product tentatively identified as a thiazolidine derivative of glutathione. It is suggested that this derivative, which only forms above pH 6·5, is produced by reaction between glutathione (GSH) and the thiocarbonyl chloride liberated on the decomposition of captan. Captan toxicity could not be completely reversed by pretreatment with thiols and disulphides capable of penetrating the cell membrane, confirming the previous hypothesis that fungitoxicity is due to irreversible changes following the oxidation of the protein thiols to disulphides.