LAUSR

Respiratory supercomplex factor (Rcf) 1 is a membrane‐bound protein that modulates the activity of cytochrome c oxidase (CytcO) in Saccharomyces cerevisiae mitochondria. To investigate this regulatory mechanism, we studied the interactions of CytcO 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 rcf1Δ mitochondria, a significant fraction remains oxidized. Upon addition of ascorbate in the presence of O2 and KCN, the reduction level of hemes a and b was a factor of ~ 2 larger with the wild‐type than with the rcf1Δ mitochondria. These data indicate that turnover of CytcO was less blocked in rcf1Δ than in the wild‐type mitochondria, suggesting that Rcf1 modulates the structure of the catalytic site.