Evidence that the mitochondrial activator of phosphorylated branched-chain 2-oxoacid dehydrogenase complex is the dissociated E1 component of the complex.

Branched-chain 2-oxoacid dehydrogenase complex is inactivated by phosphorylation of the alpha-subunit of the E1 component of the complex. High-speed supernatant from rat liver mitochondria contains an activator protein which can restore activity to the phosphorylated complex without concomitant dephosphorylation [(1982) FEBS Lett. 147, 35-39]. We report here several lines of evidence which indicate that activator is the dissociated non-phosphorylated form of the E1 component.