Immunochemical identification of branched-chain 2-oxo acid dehydrogenase kinase.

Branched-chain 2-oxo acid dehydrogenase kinase was characterized using anti-kinase polyclonal antibodies. The antibodies were purified from rabbit antiserum by an epitope selection method. The antibodies bound only to a 44 kDa polypeptide in the dehydrogenase-kinase complex and inhibited the kinase activity, substantiating that the 44 kDa polypeptide is the catalytic subunit of the kinase. The purified liver dehydrogenase-kinase complex, but not either the purified heart complex or the partially purified liver complex, contained 2 additional polypeptides of lower molecular weight which also reacted with the anti-kinase antibodies, suggesting that the liver kinase is subject to proteolytic degradation during purification.