Interaction of benzimidazole‐N‐sulfonamides with the cytochrome b/c1 complex of Pythium aphanidermatum

Experiments with intact cells and submitochondrial fractions of Pythium aphanidermatum (Edson) Fitz. indicated an interference of benzimidazole‐N‐sulfonamides with the NADH‐ or succinate‐driven electron transport system between cytochromes b and c. Comparison with Ustilago maydis (DC) Corda and Botrytis cinerea Pers. ex Fr. revealed that this effect is Oomycetes specific. The molecular interaction between benzimidazole‐N‐sulfonamides and the mitochondrial cytochrome b/c1 complex from P. aphanidermatum has been investigated. Binding assays with [14C]52232 RP (dimefluazole) indicated a time‐ and dose‐dependent labelling of two proteins. The molecular mass of one labelled protein and the competition of the binding with antimycin A suggest that benzimidazole‐N‐sulfonamides interact with the Q1‐centre of cytochrome b. Furthermore, experiments with doubly labelled [3H][14C]CGA 323103 revealed a possible irreversible inactivation of the b/c1 complex leading to covalent linkage of the dimethylsulfonamoyl moiety to the target site.