title: Properties of phosphatidylinositol kinase of human platelets.
abstract: We have previously reported that phosphatidylinositol (PI) kinase of intact platelet may be activated by either elevating intracellular cAMP content or lowering cytosolic Ca2+ (Thrombos. Res. 44, 155, 1986). Further studies were conducted to elucidate properties of platelet PI-kinase, especially possible regulation by A-kinase or Ca2+. The activity of the enzyme in platelet homogenate was markedly inhibited by a very low Ca2+, while Mg2+ was absolutely required for the activity. The activity was not affected by the presence of A-kinase catalytic subunit or protein kinase inhibitor but it was inhibited by cAMP as well as other compounds containing adenosine. These results suggest that the platelet PI-kinase is not regulated directly by A-kinase but by Ca2+ and that the regulation by Ca2+ may act as a negative feedback system in activated platelets.
authors.affiliation: Second Department of Surgery, Osaka University Medical School, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Suga
authors.forename: J
authors.initials: J
authors.lastname: Kambayashi
authors.forename: T
authors.initials: T
authors.lastname: Tsujinaka
authors.forename: M
authors.initials: M
authors.lastname: Sakon
authors.forename: T
authors.initials: T
authors.lastname: Mori
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase; D001081:Apyrase / Q000378:metabolism; D001792:Blood Platelets / Q000201:enzymology*; D002118:Calcium / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D010743:Phospholipids / Q000097:blood; D010770:Phosphotransferases / Q000097:blood*
chemical_list: D010743:Phospholipids; D010770:Phosphotransferases; D019870:1-Phosphatidylinositol 4-Kinase; D001081:Apyrase; D008274:Magnesium; D002118:Calcium