title: Identification and characterization of the phosphatidylinositol kinase in membranes of murine T lymphocytes.
abstract: Polyphosphoinositide metabolism appears to be a widely employed mechanism by which membrane receptors transduce the signal to activate cells. This pathway has been implicated in the activation of T lymphocytes. Unlike many receptor systems in which decreased levels of polyphosphoinositides are observed, T lymphocytes demonstrate increased concentrations of polyphosphoinositides as well as phosphoinositols (particularly IP3) on activation by mitogens. To understand the early biochemical events involved in T cell activation, we sought to identify and characterize the enzyme responsible for phosphorylating phosphatidylinositol (PI) to phosphatidylinositol 4-phosphate (PIP) in murine T lymphocytes. This kinase was found to be an integral membrane protein of T lymphocytes. It was found to be Mg2+ (apparent Km = 5 mM)- or Mn2+-dependent, whereas Ca2+ was noted to be a competitive inhibitor of Mg2+. ATP is the preferred substrate over GTP (apparent Km = 0.14 mM and 0.62 mM, respectively). The kinase is inhibited by both PIP and PI 4,5-bisphosphate (PIP2), but not by other phospholipids or angiotensin II (a substrate for tyrosine kinase). The enzyme activity has identical characteristics in membranes derived from a T cell hybridoma, thymocytes, and T cell clones. The enzyme migrated predominantly as a single peak with an apparent m.w. of approximately 60,000 on gel filtration chromatography. The relationship of this enzyme to viral oncogene products such as pp60v-src and p68v-ros is discussed.
mesh_terms: D019870:1-Phosphatidylinositol 4-Kinase; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002458:Cell Fractionation; D002462:Cell Membrane / Q000201:enzymology; D002850:Chromatography, Gel; D006358:Hot Temperature; D006825:Hybridomas / Q000201:enzymology; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000494:pharmacology; D010770:Phosphotransferases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D013347:Subcellular Fractions / Q000201:enzymology; D013379:Substrate Specificity; D013601:T-Lymphocytes / Q000201:enzymology*
chemical_list: D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; C037178:phosphatidylinositol 4-phosphate; D000255:Adenosine Triphosphate; D010770:Phosphotransferases; D019870:1-Phosphatidylinositol 4-Kinase; D008274:Magnesium; D002118:Calcium