Comparison of abundant cytosol proteins in rat liver, Novikoff hepatoma, and Morris hepatoma by two-dimensional gel electrophoresis.

Following the recent demonstration of differences in mRNA species in the Novikoff hepatoma and normal rat liver (2), a search was made for differences in the abun dant cytosol proteins of these tissues as well as of several Morris hepatomas and other rat tissues. With the aid of 2dimensional electrophoresis, it was found that each of the nontumorous tissues had a distinctive pattern of abundant proteins. Protein 56/8.3 (molecular weight/isoelectric point) was present in all of the tissues studied; its spot size and density were proportional to protein synthesis and/or growth rate. The 2-dimensional electrophoretic migration of Protein 56/8.3 is very similar to Elongation Factor 1«of protein synthesis. The fastest-growing tu rners, Morris hepatoma 3924A and the Novikoff hepatoma, contain a large number of proteins that have not been found in normal liver; their 13 common proteins included Proteins 72/6.8, 64/7.3, 45/7.8, and 35/7.7, which were not found in other tissues. Interestingly, these fast-growing tumors also differed markedly in the other proteins of their patterns. Only Protein 79/6.7 was common to all of the tumors studied and was not present in nontumorous tissues. In the slow-growing Morris hepatomas 9618A and 8999, the protein patterns were very similar to that of normal liver; only 4 abundant proteins differed from those of the normal liver. A group of 11 proteins in the 61-69/6.57.5 region was prominent in the liver and slowly growing hepatomas; this group of proteins was absent from the rapidly growing tumors. These results are in agreement with previous reports that have demonstrated many biochemical similarities of slow-growing Morris hepatomas and normal liver. Also, it is apparent that increasing growth rate is associated with concomitant alteration in the abundance of special pro teins. These special proteins differ from those of normal liver and slow-growing hepatomas.