Properties and purification of a glucose-regulated protein from chick embryo fibroblasts

A glucose-regulated protein of molecular weight 78,000 (GRP-78) had been purified from a membrane fraction isolated from viral transformed chick embryo fibroblasts. Purification was achieved by extraction of the membrane fraction with Triton X-100, and chromatography on diethylaminoethyl-cellulose and hydroxyapatite. The purified protein exhibited one single spot on two-dimensional polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and has a pI of about 5.3. A monospecific antiserum to GRP-78 was generated in a goat. Immunofluorescence studies using affinity purified antibodies to GRP-78 revealed that this protein was not exposed on the cell surface but was localized in a granular vesicular network inside the cell that resembles the distribution of endoplasmic reticulum. The availability of purified GRP-78 and a specific antiserum to it should prove useful in elucidating the role of this protein in glucose metabolism and its relationship to malignant transformation.