Metabolism of phosphoinositides in the rat erythrocyte membrane. A reappraisal of the effect of magnesium on the 32P incorporation into polyphosphoinositides.

The metabolism of phosphoinositides was investigated in the red blood cell membrane of the rat by measuring 32P-incorporation into phospholipids after incubation of membranes with [gamma-32P]ATP in a medium containing magnesium. A new chromatographic procedure has been developed which facilitates the separation of triphosphoinositide, diphosphoinositide and phosphatidylinositol from the phospholipids present in lipid extracts of incubated 'ghost' under our experimental conditions only two phospholipids, diphosphoinositide and triphosphoinositide, were 32P-labelled. Furthermore, the results indicate that either di-or triphosphoinositide could be labelled preferentially, depending upon the magnesium concentration of the incubation medium. This clarifies some apparent discrepancies reported in the literature between the 32 P labelling of polyphosphoinositides observed in intact erythrocytes and that observed with 'ghost' membranes. In addition, the enzymatic pathways involved in the phosphoinositide metabolism are discussed.