Calcium ion dependent interaction of inorganic phosphorus compounds with phosphatidylcholine

The translocation of orthophosphate, pyrophosphate, and polyphosphate into an organic phase was examined by means of the two-phase partition method. When the organic phase contained phosphatidylcholine (PtdCho), the phosphorus compounds translocated from the water-phase into the organic phase, depending on the concentrations of PtdCho and Ca2+, and the pH of the solution. Calcium ions were essential for the translocation. The concentration of Ca2+ necessary for the translocation appeared to depend on the molar concentration of the phosphorus compounds. Orthophosphate was translocated above pH 6.5, while pyrophosphate was translocated above pH 3.5. In contrast, polyphosphate was translocated in the whole pH range examined (pH 2.5-9.0), although approx. 9% of the total polyphosphate remained in the water-phase even at alkaline pH. These results suggest that phosphorus compounds can interact with PtdCho when the phosphorus compounds have formed complexes with Ca2+.