The human erythrocyte contains two forms of phosphatidylinositol-4-phosphate 5-kinase which are differentially active toward membranes

Abstract

A human erythrocyte cytosolic phosphatidylinositol-4-phosphate 5-kinase (PIP kinase) and a membrane-bound PIP kinase have been purified by phosphocellulose chromatography. Fractionation of the membrane-bound PIP kinase activities by phosphocellulose separated activity into two peaks, which eluted at 0.6 M NaCl (type I PIP kinase) and 1.0 M NaCl (type II PIP kinase). The cytosolic PIP kinase and the membrane-bound type II PIP kinase are 53 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, have indistinguishable 125I-peptide maps, and are immunochemically indistinguishable, suggesting that they are sequence identical. Antibodies raised to the cytosolic PIP kinase inhibit activity of both the membrane-bound type II and the cytosolic PIP kinases. The type I PIP kinase appears to be distinct from the cytosolic and membrane-bound type II PIP kinase; it is not immunocross-reactive, and antibodies toward type II PIP kinases do not inhibit type I PIP kinase. Further, membrane-bound type II PIP kinase can be removed from type I PIP kinase without loss of activity. Functional characterization of the PIP kinases demonstrates that the type I kinase has a 10-fold lower Km for PIP and a 5-fold higher Km for ATP compared with the type II enzymes. The type I and type II (membrane-bound or cytosolic) PIP kinases are modulated differentially by spermine and heparin. Finally, the type I PIP kinase phosphorylates intrinsic PIP on isolated erythrocyte membranes, whereas the type II PIP kinases have no activity toward native membranes.