Phosphorylation and degradation of exogenous phosphatidylinositol incorporated into Friend erythroleukemic cells.

Abstract

Phosphatidyl[2-3H]inositol (PtdIns) obtained from rat skeletal muscle and yeast was introduced into Friend erythroleukemic cells by use of the PtdInstransfer protein or by spontaneous route. The mammalian PtdIns incorporated by the transfer protein appeared metabolically inert while the spontaneously incorporated PtdIns was both phosphorylated to PtdIns-4-phosphate (i.e. 30% of the total PtdIns incorporated) and converted into lyso-PtdIns (i.e. 20% of the total PtdIns incorporated); formation of PtdIns, 4,5-bisphosphate was minimal. The extensive metabolism of the spontaneously incorporated PtdIns strongly suggests that this PtdIns does not rapidly equilibrate with the endogenous PtdIns pools. A similar spontaneous incorporation of yeast PtdIns was accompanied by a negligible degree of phosphorylation and hydrolysis. Evidence is provided that this difference in metabolism reflects the absence of arachidonate in the yeast PtdIns.