Characterization of a pyruvate dehydrogenase modulator purified from insulin-treated rat brain plasma membranes

A factor able to stimulate pyruvate dehydrogenase when added to purified mitochondria was prepared from the supernatant of brain plasma membranes incubated with physiological concentrations of insulin (25 microU/ml). The factor completely reactivated pyruvate dehydrogenase previously inhibited with ATP and was active on pyruvate dehydrogenase from brain and liver mitochondria and from peripheral lymphocytes. The insulin-dependent stimulator of pyruvate dehydrogenase was heat and acid stable, was not absorbed on charcoal and displayed an isoelectric point of 5.5. The insulin mediator was purified by gel filtration, DEAE-cellulose and sulfonated polystyrene chromatography and, after dansylation, by high performance liquid chromatography. The purified mediator displayed a molecular weight of about 2800 and appeared as a peptide rich in glycine and serine and void of proline and sulfur containing aminoacids. It retained its stimulatory action on pyruvate dehydrogenase after dansylation and was completely inactivated by trypsin and chymotrypsin. Full reactivation of ATP-inhibited pyruvate dehydrogenase was attained when mitochondria were incubated with a mediator concentration of about 0.5 microM.