Isolation, characterization and function of the two cytochromes c of the yeast Candida parapsilosis

Candida parapsilosis is a strictly aerobic yeast which possesses two respiratory chains with a peculiar organisation, different from that of plant mitochondria. Besides the classical electron transport pathway, mitochondria of C. parapsilosis develops an alternative pathway, which does not branch off at the ubiquinone level, but merges at the complex IV level. Two pools of cytochromes c were distinguished by their spectrometric and potentiometric properties: (i) sequential cytochrome c reduction was promoted by two substrates, PMS (Em = 70 mV) and TMPD (Em = 280 mV). TMPD promoted the reduction of a cytochrome c with maxima at 551.9 and 417.3 nm for the alpha and the Soret bands, respectively, whereas cytochrome c reducible by PMS exhibited maxima at 549.7 and 419.9 nm; (ii) two midpoint redox potentials were resolved at 180 mV and 280 mV, respectively. The two cytochromes c were copurified by ion-exchange chromatography on Amberlite; after this step, the two cytochromes c can always be differentiated by TMPD and PMS, these reductants promoting different absorption bands. The two cytochromes c were separated by reverse-phase HPLC; this last purification step resolved two proteins with the same relative molecular mass of 13600 but a different amino-acid composition. Comparison of N-terminal sequences revealed differences between the two proteins. It was hypothesized that one cytochrome c is implicated in the functioning of the main chain and the other in that of the secondary pathway.