A LOW-MOLECULAR-WEIGHT SUBSTANCE PURIFIED FROM HUMAN PLACENTA INHIBITS CAMP-DEPENDENT PROTEIN-KINASE AND ACTIVATES PROTEIN-KINASE-C

We have purified from human placenta a low molecular mass substance th at inhibits cAMP-dependent protein kinase and activates protein kinase C. This protein kinase regulator was purified in three steps: (1) hom ogenizing placentas in chloroform/methanol and extracting the regulato r into water; (2) eluting a strong anion exchange high performance liq uid chromatography (HPLC) column with a quaternary gradient; and (3) e luting a reversed-phase HPLC column with a binary gradient. The regula tor was found to be highly purified by HPLC, thin-layer chromatography (TLC) and laser desorption ionization mass spectrometry with a molecu lar mass of 703 Daltons by the latter procedure. The physical and bioc hemical properties of this protein kinase regulator suggest that it is a phospholipid but it did not co-elute by HPLC or by TLC with any of the known phospholipid activators of protein kinase C.