Calcium-phospholipid enhanced protein phosphorylation in human placenta.
Calcium-activated, phospholipid-dependent protein phosphorylation has not been studied in placenta. Human placental cytosol was subjected to an endogenous protein phosphorylation assay using [gamma-32P]ATP in the presence of calcium and phosphatidylserine. Protein phosphorylation was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. When compared to basal levels, calcium (10(-6) M) in combination with phosphatidylserine (50 micrograms/ml) significantly enhanced (P less than 0.01) 32P incorporation into phosphoproteins having mol wt 47,000, 43,000, and 37,000. Half-maximal 32P incorporation was observed with 3.5 X 10(-7) M Ca2+ in the presence of phosphatidylserine (50 micrograms/ml). The effect of phosphatidylserine was biphasic. In the presence of Ca 10(-6) M, 32P incorporation increased to a maximum at 70 micrograms/ml of phosphatidylserine. The increase was suppressed at 150 micrograms/ml. Tetracaine caused a dose-dependent inhibition of calcium-activated, phospholipid-dependent enhancement of the three phosphorproteins. Calcium in the absence of phospholipid enhanced the phosphorylation of a protein of 98,000 mol wt. Phosphatidylserine suppressed this enhancement. Calmodulin (10(-6) M) had no detectable effect upon phosphorylation beyond that of calcium alone, but the calmodulin inhibitor R-24571 specificlly inhibited the calcium-stimulated 98,000 mol wt phosphoprotein. Calcium-activated, phospholipid-dependent phosphoproteins are present in human placental cytosol; whether calcium-activated, calmodulin-dependent phosphoproteins also are present remains a question.
D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D066298:In Vitro Techniques; D010718:Phosphatidylserines / Q000494:pharmacology; D010743:Phospholipids / Q000494:pharmacology*; D010758:Phosphorus / Q000378:metabolism*; D010766:Phosphorylation; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011506:Proteins / Q000378:metabolism*; D013748:Tetracaine / Q000494:pharmacology
D007093:Imidazoles; D010718:Phosphatidylserines; D010743:Phospholipids; D011506:Proteins; D013748:Tetracaine; D010758:Phosphorus; C031938:calmidazolium; D002118:Calcium