Complete fractionation of brain cephalin; isolation from it of phosphatidyl serine, phosphatidyl ethanolamine, and diphosphoinositide.

Brain cephalin (1) has been the name given to a fraction of brain phosphatides characterized by its solubility in ether and insolubility in ethyl alcohol. For many years it was assumed to be a single compound with the chemical structure of diacylglycerylphosphoryl ethanolamine. Work from this laboratory has shown brain cephalin to be a mixture (2). From it were separated two pure phosphatides; namely, phosphatidyl ethanolamine and phosphatidyl serine. The former phosphatide has the chemical structure classically attributed to brain cephalin and the latter has been found to be oleylstearylglycerylphosphoryl serine (3). Besides these two phosphatides, a material was obtained which appeared to be a mixture and to which the name of inositol phosphatide was given for descriptive purposes, since it had inositol as a constituent. This paper contains detailed proof that inositol phosphatide is a mixture and describes a method for the separation from it of phosphatidyl ethanolamine, phosphatidyl serine, and a new inositol-containing phosphatide to which the name of diphosphoinositide has been given. Results establishing in part the chemical structure of diphosphoinositide have already been reported in a preliminary note (4) and are given in detail in the accompanying paper (5). The evidence here reported establishes that brain cephalin is a mixture of the three phosphatides mentioned above. It contains only small amounts of other substances which can be considered as contaminants. These contaminants are either lipides of the carbohydrate-containing type or non-lipide water-soluble substances among which phosphates appear to be predominant. The water-soluble contaminants can be removed by dialysis. Brain cephalin, as defmed by its solubilities, does not account for all of the lipide NH2-N’ present in brain. Not an inconsiderable amount of