Abstract
Ball, Anfinsen, and Cooper (1947) demonstrated that 2-hydroxy-3-alkylnaphthoquinones, which possess antimalarial activity, exert their inhibitory effect on respiration by inhibiting succinoxidase. They pinpointed the locus of action of these compounds to a site between cytochromes b and c in the electron transport system. The recent discovery of a benzoquinone, coenzyme Q 10 (CoQ 10), as a cofactor essential for electron transport ( Crane, Hatefi, Lester, and Widmer, 1957) prompted us to investigate the possibility that the naphthoquinones were inhibiting at the CoQ 10 site. The present communication describes studies which demonstrate that the inhibitory effect of the antimalarial naphthoquinones on the succinoxidase system of beef heart electron transport particles (ETP) can be reversed by CoQ 10 and related compounds. Antimycin A, also known to inhibit between cytochromes b and c in the electron transport chain ( Potter and Reif, 1952), is not so antagonized.
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