The comparative enzymology and cell origin of rat hepatomas. II. Glutamate dehydrogenase, choline oxidase, and glucose-6-phosphatase.

The activities of glucose-6-phosphatase, glutamate dehydrogcnase, and choline ox[dase were determined in some or all of ten rat hepatomas, including the Novikoff, Dunning L-C18, McCoy MDAB, and the Morris 3683, 39524A, and 51~3 hepatomas, together with primary hepatomas produced by feeding ethionine or 3%nethyl-4dimethylaminoazobenzene, and transplanted hepatomas derived from the primary tumors induced with ethionine. Of these neoplasms, only the Morris hepatoma 51~3, the primary and transplanted ethionine-induced hepatomas, and one of the 3'-methyl-4-dimethylaminoazobenzeneinduced tumors possessed significant glucose-6-phosphatase activity. These same tumors in addition to the Dunning L-C18 hepatoma had demonstrable glutamate dehydrogenase activity, whereas the other neoplasms tested failed to show significant activity of this enzyme. With the exception of the primary dye-induced neoplasm, which was not tested, only those neoplasms having significant glucose-6-phosphatase activities showed any choline oxidase activity. Of those neoplasms tested for tryptophan peroxidase activity only the Morris hepatoma 51~3, the primary ethionine-induced hepatoma, and some of the Dunning L-C18 hepatomas had any demonstrable activity of this enzyme. In contrast to most of the enzymatic activities reported here, the threonine dehydrase activity of the Morris hepatoma 51r was of the order of 40 times the level of this enzyme in the livers of animals bearing this tumor. The significance of these results in relation to the biochemical and morphologic classification of experimental hepatic carcinomas, as well as the importance of studying the biochemistry of slowly growing, highly differentiated experimental neoplasms such as the Morris hepatoma 51~3, is discussed.