A NOVEL ACIDIC FORM OF THE PHOSPHATIDYLINOSITOL TRANSFER PROTEIN IS PREFERENTIALLY RETAINED IN PERMEABILIZED SWISS MOUSE 3T3 FIBROBLASTS

By use of indirect immunofluorescence it was shown that phophatidylino sitol transfer protein (PI-TP) remains associated with the Golgi syste m of Swiss mouse 3T3 fibroblasts after permeabilization with streptoly sin 0. By Western blot analysis it was demonstrated that intact cells contain the phosphatidylinositol-bound form of PI-TP (pI 5.5) and a no vel more acidic form of PI-TP (pI 5.4) in approximately equal amounts. After permeabilization, about 50% of the PI-TP was retained in the ce lls with an enrichment of the pH 5.4 form relative to the pH 5.5 form; the opposite was observed for the PI-TP released into the medium. Sub fractionation of cell homogenates by centrifugation provided evidence that a distinct amount of PI-TP is strongly bound to the membrane frac tion with the pH 5.4 form more prominently present than the pH 5.5 for m. (c) 1994 Academic Press, Inc.