Inositol Phosphorylceramide, a Novel Substance and the Chief Member of a Major Group of Yeast Sphingolipids Containing a Single Inositol Phosphate

Abstract About one-third of the nondeacylatable phospholipids in Saccharomyces cerevisiae have been shown to be a group of sphingolipids with a single phosphoinositol moiety. This group of lipids was obtained richly concentrated in high yield by several simple steps involving differential solubility. Four components of this group were further purified by liquid chromatography on base-treated porous silica beads. The major component of this group proved to be the novel substance, inositol phosphorylceramide, the ceramide consisting of hydroxysphinganine and a hydroxy C-26 fatty acid. Two other inositol phosphorylceramides were purified which differed from the major component in their ceramide moieties. Two glycolipids are minor members of this group of monoinositol-containing sphingolipids and one of these was purified, and had a composition consistent with its formulation as a mannosylinositol phosphorylceramide. The major inositol phosphorylceramide could be cleaved quantitatively by alkali to give an inositol monophosphate and could be cleaved by periodate to give a C-15 fragment. Periodate treatment followed by borohydride reduction and HCl hydrolysis gave a significant yield of phosphoserinol. These facts suggest strongly that the phosphoinositol moiety is attached to position 1 of the hydroxysphinganine. Data obtained with cells uniformly labeled with [3H]-inositol suggest that all significant ( g 1% lipid 3H) inositol-containing lipids in yeast have now been chemically characterized.