Energy conversion coupled to cyanide-resistant respiration in the yeasts and

Cyanide-resistant respiration (CRR) is a widespread metabolic pathway among yeasts, that involves a mitochondrial alternative oxidase sensitive to salicylhydroxamic acid (SHAM). The physiological role of this pathway has been obscure. We used the yeasts Debaryomyces hansenii and Pichia membranifaciens to elucidate the involvement of CRR in energy conversion. In both yeasts the adenosine triphosphate (ATP) content was still high in the presence of antimycin A or SHAM, but decreased to low levels when both inhibitors were present simultaneously, indicating that CRR was involved in ATP formation. Also the mitochondrial membrane potential (Delta Psi(m)), monitored by fluorescent dyes, was relatively high in the presence of antimycin A and decreased upon addition of SHAM. In both yeasts the presence of complex I was confirmed by the inhibition of oxygen consumption in isolated mitochondria by rotenone. Comparing in the literature the occurrence of CRR and of complex I among yeasts, we found that CRR and complex I were simultaneously present in 12 out of 13 yeasts, whereas in six out of eight yeasts in which CRR was absent, complex I was also absent. Since three phosphorylating sites are active in the main respiratory chain and only one in CRR, we propose a role for this pathway in the fine adjustment of energy provision to the cell.