The energetic growth yields of the yeast Candida parapsilosis

The energetic growth yields of Candida parapsilosis were compared with those of Saccharomyces cerevisiae as a function of the energy source in the presence or absence of antimycin A, an inhibitor of the second phosphorylation site. When glycerol was used as energy source, the energetic growth yields were quite similar in C. parapsilosis and S. cerevisiae. On the other hand, when experiments were carried out with glucose as energy source, although three phosphorylation sites were available, glucose was found to be a poor energy source for C. parapsilosis. When C. parapsilosis was grown in the presence of antimycin A, on glucose: YGluS = 3YGlu + AS and on glycerol: YGlyS = 2 YGly + AS. It was concluded that growth in the presence of antimycin A could occur due to the functioning of the third phosphorylation site. This result agrees with previous works indicating that in C. parapsilosis the alternative pathway merges into the main respiratory chain at the cytochrome c level. Although the doubling time of C. parapsilosis was much less temperature-sensitive than that of S. cerevisiae, the energetic growth yield was the same at 13 degrees C and 28 degrees C, and consequently, the secondary pathway did not seem to be thermogenic.