Modulation of O 2 reduction in Saccharomyces cerevisiae mitochondria

Respiratory supercomplex factor (Rcf) 1 is a membrane‐bound protein that modulates the activity of cytochrome c oxidase (Cyt c O) in Saccharomyces cerevisiae mitochondria. To investigate this regulatory mechanism, we studied the interactions of Cyt c O with potassium cyanide ( KCN ) upon removal of Rcf1. While the addition of KCN to the wild‐type mitochondria results in a full reduction of heme a , with the rcf1 Δ mitochondria, a significant fraction remains oxidized. Upon addition of ascorbate in the presence of O 2 and KCN , the reduction level of hemes a and b was a factor of ~ 2 larger with the wild‐type than with the rcf1 Δ mitochondria. These data indicate that turnover of Cyt c O was less blocked in rcf1 Δ than in the wild‐type mitochondria, suggesting that Rcf1 modulates the structure of the catalytic site.