Protein phosphorylation in human placenta. Stimulation by epidermal growth factor.

Membranes prepared from normal human term placenta possess a protein kinase activity which phosphorylates endogenous substrates in the presence of [gamma-32P]ATP. This kinase activity requires either Mg2+ or Mn2+, is enhanced by glycerol and appears to be cyclic-nucleotide-independent. Addition of epidermal growth factor to the placental membrane preparation increases the level of total phosphorylation by approx. 35%. When analyzed by sodium dodecyl sulfate gel electrophoresis and autoradiography, the placental proteins whose degree of phosphorylation was enhanced by epidermal growth factor had apparent molecular weights of 170000, 150000, and 25000. This report documents the presence of protein kinase activity in human placenta and demonstrates that epidermal growth factor can enhance protein phosphorylation in normal human tissue.