The α subunit of the E1 component of branched-chain 2-oxoacid dehydrogenase complex becomes rapidly phosphorylated in rat liver, kidney and heart mitochondria incubated in the presence of succinate and [32P]phosphate. Peptide mapping of tryptic digests of the phosphorylated α subunit indicates that 3 distinct sites are phosphorylated, as has been reported previously by us for phosphorylation in vitro of highly purified complex.
