Protein turnover in microsomal subfractions of liver and Morris hepatomas 7800 and 9618A.

pared 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 tl/2 values were observed among the respective subfractions of a given liver or tumor, when compared with one another. The half-lives of the microso mal 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 mo lecular weight in the host liver, whereas the same protein fractions in the hepatomas did not vary with molecular size and showed extended /,/2 values. Most tl/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 hepa toma, the data also support the concept that degradation of individual membrane proteins is largely dissociated from the degradation of the total paniculate membrane.