Turnover of Phosphatidic Acid and Sodium Extrusion from Mammalian Erythrocytes

Phosphatidic acid (PA) from swine and beef RBCs was isolated by chromatography on silicic acid columns. It comprised about 1 per cent of the total lipid phosphate in RBCs, but was eluted nearly pure from columns. An uncharacterized inositide accounted for 5 to 10 per cent of the phosphate in the PA-containing fraction. When cells were incubated with HP³²O₄⁼, the fraction containing PA became more radioactive than any of the other fractions obtained. However, analysis of the labeled material by paper chromatography showed that most of the P³² was in the inositide, not in PA. With the assumption of kinetic homogeneity for cellular PA, compartmental analysis of the kinetics of tracer incorporation showed that PA turnover is 3 to 4 orders of magnitude too slow to account for sodium extrusion by these cells.