Purification and characterization of cytosol protein 45/7.8 present in rapidly growing hepatomas

Protein 45/7.8 (molecular weight X 10(-3)/isoelectric point) was found in the cytosol of several rapidly growing hepatomas including Morris hepatomas 3924A and 9618A2 and Novikoff hepatoma. It was not found in Morris hepatomas 7794A and 8999, which have intermediate growth rates, or in the slow-growing Morris hepatoma 9618A, normal rat liver, 18-hr regenerating rat liver, or livers of fetal rats. Protein 45/7.8 was isolated under nondenaturing conditions from Morris hepatomas 3924A and 9618A2 and Novikoff hepatoma in high purity by purification in three steps: ammonium sulfate fractionation; diethylaminoethyl cellulose chromatography; and hydroxylapatite chromatography. The protein was highly purified as shown by two-dimensional, isoelectric-focusing sodium dodecyl sulfate:polyacrylamide gels. The amino acid composition of protein 45/7.8 from the three tumors studied was very similar; the acid of protein 45/7.8 was proline, and its COOH terminus amino acid was tyrosine. Protein 43/8.1 found in normal liver is different from hepatoma protein 45/7.8 by amino terminus, amino acid composition, and tryptic peptides.