Demonstration of a Pyruvate Dehydrogenase Activator in Insulin-Treated Human Placental Plasma Membrane

A factor capable of activating pyruvate dehydrogenase (PDH) was found in human placental plasma membrane, which is known to be rich in insulin receptors. This factor was isolated from insulin-treated plasma membrane fraction, and its activity was demonstrated after Sephadex G-25 gel chromatography. The activity of PDH was assayed using mitochondrial fractions from rat adipocytes and hepatocytes. A significant stimulation of PDH activity occurred by addition of the gel filtration fractions of the extract corresponding to l,O00-l,500 daltons from insulin-treated placental plasma membrane. This activity was acid-and heat-stable but inactivated by treatment with trypsin or chymotrypsin, suggesting that it is a peptide. We conclude that an insulin-dependent PDH activator, similar to that of adipocytes, exists also in human placenta.