Regulation of bovine kidney branched-chain 2-oxoacid dehydrogenase complex by reversible phosphorylation

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Abstract
Bovine kidney mitochondrial branched-chain 2-oxoacid dehydrogenase complex is inactivated by covalent phosphorylation catalyzed by a specific protein kinase intrinsic to the complex. Tryptic digestion of phosphorylated complex releases 3 phosphopeptides, indicative of multisite phosphorylation. These 3 tryptic peptides contain only 2 sites of phosphorylation which are closely grouped on the .alpha. subunit of the E1 component of the complex. The amino acid sequence of the phosphorylated region was determined. Conditions were developed which allow investigation of the phosphorylation and dephosphorylation of the 2 sites. Both sites can be dephosphorylated at significant rates in vitro by 2 cytosolic protein phosphatases, namely phosphatases 2A and 2C. Dephosphorylation of one site correlated closely with re-activation of the complex.