21] Phosphatidylinositol-4-phosphate 5-kinases from human erythrocytes

Abstract

Publisher Summary Polyphosphoinositides play a crucial role in cellular signal transduction. Phosphatidylinositol (PI) undergoes a series of phosphorylations to give phosphatidylinositol phosphate (PIP) and further phosphatidylinositol bisphosphate (PIP 2 ), which produces two second messengers—1,2-diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP 3 )—mediating Ca 2+ mobilization in response to many hormones, neurotransmitters, and growth factors. The chapter explains the preparation of two distinct forms of PIP kinases from human erythrocyte membranes and cytosol, their one-step purification on a phosphocellulose column, and the study of their structural and functional properties. In all cells and tissues so far studied, the PIP kinase has been found both as a cytosolic and as a membrane-bound enzyme. The erythrocyte cytosolic and the membrane-bound type II PIP kinases have identical or very similar structural properties. It appears that the PIP kinases are regulated by distinct pathways. Phospholipase C is regulated by guanosine-5'-triphosphate (GTP)-binding proteins or by tyrosine phosphorylation, and analogous mechanisms may regulate PIP kinase activity toward membranes.