[The systemic fungicide tridermorph as an inhibitor of the respiratory chain of electron transfer particles from beef heart mitochondria].

Tridemorph (N-tridecyl-2,6-dimethylmorpholine) inhibits both the NADH-oxidase and the succinate-cytochrome c oxydoreductase system of non-phosphorylating electron transfer particles from beef heart. The concentration required for half-inhibition amounted to 3,4 muM and 24 muM respectively. Two different sites of action in the respiratory chain could be localized by means of difference spectroscopy and measurements of enzymic activities in various partial systems. The inhibition of the NADH-ubiquinone oxydoreductase activity as well as the suppression of the NADH-induced reduction of all cytochromes on the one hand and the insensitivity of the NADH-ferricyanide oxydoreductase system on the other argue in favour of a site of action similar to rotenone. The partial suppression of the succinate-induced reduction of cytochrome b with simultaneous complete inhibition of the reduction of the other cytochromes indicate an additional site of action analogous to antimycin A. Both inhibitory actions appeared instantaneously after the addition of tridemorph and were counteracted by serum albumin. Furthermore, tridemorph inhibited the oxydation of external ferrocytochrome c but not that of ascorbate/tetra-methyl-p-phenylene-diamine-HCI (TMPID) showing that it is not a true inhibitor of the cytochrome oxidase. The TMPD-induced bypass of the succinate oxidation was inhibited as well. The possible role of the inhibition of the main pathway of the respiratory chain for the fungicidal action of tridemorph is discussed.