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Protein Turnover in Microsomal Subfractions of Liver and Morris Hepatomas 7800 and 9618A¹

Departments of Oncology and Pathology, and the McArdle Laboratory for Cancer Research, University of Wisconsin Medical School, Madison, Wisconsin 53706

The loss of label from three microsomal subfractions of Morris hepatomas 7800 and 9618A following i.v. administration of leucine-1-¹⁴C was found to be decreased, compared with that of normal liver. However, the rate of degradation of membrane protein in the 7800 hepatoma was more rapid than that in its host liver, while the proteins of the reticular membranes of the Morris 9618A hepatoma decayed at a slower rate than did those of its host liver. Despite the varied decay rates, the yields of microsomal membrane protein from the hepatomas were diminished in all instances, compared with those of normal liver. No differences in the t_1/2 values were observed among the respective subfractions of a given liver or tumor, when compared with one another. The half-lives of the microsomal fractions of host and normal lives were approximately 35 and 20 hr, respectively. Half-lives of the sodium dodecyl sulfate-solubilized microsomal proteins, as fractionated by polyacrylamide electrophoresis, varied inversely with molecular weight in the host liver, whereas the same protein fractions in the hepatomas did not vary with molecular size and showed extended t_1/2 values. Most t_1/2 values obtained for the electrophoretically separated proteins were in the same range as the overall decay rate exhibited by the fraction. While these results suggest random defect(s) in the control of degradation of membrane proteins of the hepatoma, the data also support the concept that degradation of individual membrane proteins is largely dissociated from the degradation of the total particulate membrane.

¹ The work reported herein was supported in part by Grant CA-07175 from the National Cancer Institute and by Grant E-588 from the American Cancer Society.

² Study performed in partial fulfillment of the requirements for the Ph.D. degree at the University of Wisconsin, Madison, Wis. Trainee in Biochemical Pathology of the National Institute of General Medical Sciences (GM-00130). Present address: Department of Pathology, University of California at Los Angeles, Los Angeles, Calif.

Received 1/ 5/73. Accepted 3/12/73.