UK-2A is a potent antifungal antibiotic isolated from
Streptomyces sp. 517-02 and its structure is highly similar to that of antimycin A. We investigated the inhibition mechanism of bovine heart mitochondrial cytochrome
bc1 complex by the UK-2 A using antimycin A and myxothiazol as the reference inhibitors of ubiquinol oxidation (Q
o) and ubiquinone reduction (Q
i) sites, respectively. The inhibitory potency of UK-2A was about 3-fold less than antimycin A. On the basis of the effects of UK-2A on the reduction kinetics of
b and
c1 hemes, this compound appeared to be an inhibitor of the Q
i site. However, since spectral changes of dithionite-reduced Cytochrome
b induced by UK-2A binding differed from that of antimycin A, the precise binding manner of UK-2 A to the enzyme is not identical to that of antimycin A. It could be concluded that antimycin A binding to cytochrome
b is primarily decided by structural specificity of the salicylic acid moiety.
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