The antimycin-A-insensitive respiratory pathway of Candida parapsilosis: evidence for a second quinone involved specifically in its functioning.

The involvement of a quinone in the antimycin A-insensitive electron transfer from NADH-dehydrogenase to cytochrome c via the alternative respiratory chain of Candida parapsilosis, by-passing complex II, has been studied. After a partial extraction of quinones, the residual respiration was fully antimycin-A-sensitive, but reincorporation of the organic extract partially restored an antimycin A-insensitive respiration. Analysis of quinone content by HPLC, after purification by thin-layer chromatography, evidenced another quinone species in a very low amount. Myxothiazol and stigmatellin were shown to inhibit the alternative pathway but at a higher concentration than required to inhibit the classical pathway. Cytochrome spectra analysis showed that, in the presence of high myxothiazol concentrations, cytochromes c and aa3 were not reduced, while they were in the presence of antimycin A. It is suggested that the secondary pathway of C. parapsilosis involved a specific quinone pool which can be displaced from its binding site by high concentrations of myxothiazol or analogous compounds.