Non-choline-containing phospholipids solubilize divalent metal ions in organic solvents. The basis for a sensitive...

Phospholipids which do not contain choline were found to solubilize Ni(II) in the chloroform phase resulting from the Folch extraction procedure. On the basis of this phenomenon a radioactive assay for such phospholipids was developed using 63Ni(II). This assay can be made rather sensitive by scaling down and can be performed relatively rapidly. The disadvantages are that it does not measure phosphatidyl chlorine or sphingomyelin and that different phospholipids bind different amounts of Ni(II). Alternatively, non-choline-containing phospholipids can be assayed colorimetrically on the basis of their ability to solubilize Cu(II) in the chloroform phase. The failure of phosphatidyl choline and sphingomyelin to bind divalent cations may be due to formation of an intramolecular salt between the negatively charged phosphate group and the positively charged nitrogen.