Isolation and characterization of a cytosol protein (64/7.2) present in large amounts in rapidly growing hepatomas

Protein 64/7.2 (molecular weight/isoelectric point) is present in the cytosol of several hepatomas including the Novikoff hepatoma and Morris hepatomas 9618A, 7794A, and 3924A, but it is not present in liver or 18-hr regenerating liver. Quantitatively, its concentration was highest in Novikoff hepatoma (150 microgram/g tissue) and Morris hepatoma 3924A (550 microgram/g tissue), which are rapid-growing tumors, less in Morris hepatoma 7794A (72 microgram/g tissue), which is of intermediate growth rate, and least in the slow-growing Morris hepatoma 9618A (25 microgram/g tissue). Protein 64/7.2 was isolated from Novikoff hepatoma ascites cells in high purity as shown by its migration as a single band on one-dimensional acid-urea-polyacrylamide gels and a single spot on two-dimensional isoelectric focusing sodium dodecyl sulfate-polyacrylamide gels. Its amino acid composition has an acidic to basic amino acid ratio of 1.6. Its amino-terminal amino acid is lysine, and its carboxyl-terminal amino acid is glycine. Interestingly, the amino acid composition is strikingly similar to that of the phosphorylated Novikoff hepatoma chromatin Protein Cg', partially characterized in our laboratory.