Subcellular localization and enzymatic properties of rat liver phosphatidylinositol-4-phosphate kinase.
The phosphatidylinositol-4-phosphate kinase activity in rat liver showed a subcellular distribution different from that of phosphatidylinositol kinase. It was preferentially associated with plasma membrane-rich subcellular fractions, while no or minimal activity could be ascribed to mitochondria, lysosomes, Golgi membranes or the endoplasmic reticulum. The plasma membrane enzyme phosphorylated endogenous and exogenously added phosphatidylinositol 4-phosphate at comparable initial rates. The phosphorylation of endogenous substrate was strongly inhibited by Triton X-100, while the phosphorylation of added substrate was enhanced, suggesting that endogenous phosphatidylinositol 4-phosphate was readily available to the enzyme in unperturbed plasma membranes. The total activity of phosphatidylinositol-4-phosphate kinase in rat liver was only 1/20 that of phosphatidylinositol kinase. The enzyme activity showed an unusually broad pH-optimum in the neutral range. Mg2+ was the preferred divalent cation and Km towards ATP was about 3-fold higher than the corresponding value for phosphatidylinositol kinase.
D000818:Animals; D002458:Cell Fractionation; D003902:Detergents / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008297:Male; D017830:Octoxynol; D010770:Phosphotransferases / Q000302:isolation & purification / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor); D011092:Polyethylene Glycols / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000201:enzymology
D003902:Detergents; D011092:Polyethylene Glycols; D017830:Octoxynol; D010770:Phosphotransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase