Loading rat liver mitochondria with apocytochrome c provokes exit of cytochrome c

Rat liver mitochondria were loaded with cytochrome c by incubation with large amounts of 14C]apocytochrome c. After being washed they were incubated with either more apocytochrome c or cytochrome c. There was no release of labeled proteins from the mitochondria when incubated with cytochrome c. However, there was when incubated with apocytochrome c. The material released showed only one radioactive band which migrated as cytochrome c. Also no release of proteins other than cytochrome c was detected when liver mitochondria isolated from rats injected with 35S]methionine were incubated with apocytochrome c. These results suggest that the level and possibly the turnover of cytochrome c in rat liver mitochondria is regulated by the entry of apocytochrome c into mitochondria.