The distribution of molecular species of phosphatidylinositol in ox brain and its subcellular fractions.

1. The phosphatidylinositol content of white and grey matter of ox cerebral hemispheres did not differ. The phosphatidylinositol from grey matter was slightly enriched in palmitic acid and arachidonic acid, and that from white matter was enriched in eicosatrienoic (C(20:3)) acid. These regional differences were apparently due to the greater content of myelin in the white matter, since the same tendencies were observed when combined myelinic and non-myelinic subcellular fractions prepared from the cerebral hemispheres were compared. 2. Purified phosphatidylinositol was converted into its triacetylated methylated derivative and resolved to its molecular species by t.l.c. on AgNO(3)-impregnated silica gel. The tetraenoic molecular species was predominant in phosphatidylinositol from ox cerebral hemispheres, and this feature characterized all the phosphatidylinositol samples extracted from its regions or subcellular fractions. The grey matter was more enriched in the tetraenoic species and the white matter in the trienoic species. 3. The molecular-species composition of phosphatidylinositol from the subcellular fractions of ox cerebral hemispheres was studied. The trienoic species constituted nearly one-fifth of the phosphatidylinositol from two myelinic fractions. ;Large myelin' was more enriched in this species than was ;small myelin'. Both fractions also contained greater concentrations of the dienoic species than the non-myelinic subcellular fractions. The latter fractions, one containing nuclei and the other nerve endings plus mitochondria, were enriched in the monoenoic and tetraenoic species of phosphatidylinositol. The post-mitochondrial supernatant exhibited a pattern of distribution of phosphatidylinositol species intermediate between the myelinic and non-myelinic fractions.