Two-Dimensional Gel Electrophoresis of Cytosol Phosphoproteins of Novikoff Hepatoma and Regenerating Liver¹

With two-dimensional isoelectric focusing sodium dodecyl sulfate gel electrophoresis, ³²P-labeled cytosol proteins of Novikoff hepatoma and 18-hr regenerating rat liver were separated into 133 and 129 stained polypeptides, respectively. Approximately 103 polypeptides of both tissues had essentially identical migration characteristics. Seven dense spots (molecular weight in thousands/pl) 140/6.5, 72/6.7, 64/7.2, 35/7.7, 29/7.3, 28/7.1, and 27/7.2, that were found in the Novikoff hepatoma patterns were not present in the regenerating liver patterns. Six dense spots, 50/7.0, 50/7.4, 48/6.9, 43/8.2, 33/7.4, and 25/7.4, that were found in the regenerating liver were not found in the Novikoff hepatoma. Three spots, 95/5.7, 41/6.2, and 39/6.1, common to the Novikoff hepatoma and regenerating liver were not found in the normal liver. Autoradiograms of ³²P-labeled proteins revealed 82 spots in Novikoff hepatoma and 88 spots in regenerating liver, 60 of which were common to both tissues; for Novikoff hepatoma, 5 g of cells were incubated with 300 mCi of carrier-free ³²P_i, and for regenerating liver, 100 mCi carrier-free ³²P_i were injected i.p. 15 hr after hepatectomy and 3 hr before sacrifice. Three ³²P-labeled protein spots, 65/5.8, 25/5.5, and 25/6.0, were found only in the Novikoff hepatoma and 5 spots, 55/6.1, 45/7.0, 45/7.8, 42/5.9, and 24/5.5, were found in regenerating liver. These studies extend earlier reports of differences in spot patterns of Novikoff hepatoma and normal liver cytosol using the additional parameter of ³²P-labeling as a marker for phosphoproteins.