Studies on the turnover rates of ornithine aminotransferase in Morris hepatoma 44 and host liver.

The ornithine aminotransferase [EC 2.6.1.13] content of Morris hepatoma 44 is about 15 times higher than that in normal liver. The turnover rates of ornithine amino-transferase in hepatoma 44 and host liver were determined using L-[14C]leucine. Studies on the incorporation of radioactive leucine into ornithine aminotransferase in rats bearing hepatoma 44 showed that the rate of synthesis of this enzyme in the hepatoma was about 5-fold higher than that in host liver. The half-life of ornithine aminotransferase in host liver was 0.98 day, which was the same as that in normal liver, whereas that in hepatoma 44 was 3.5 days. The rate constant of degradation of ornithine aminotransferase in hepatoma 44 was significantly less than that in host liver. These results show that the high ornithine aminotransferase content of hepatoma 44 is due to both increase in its rate of synthesis and decrease in its rate of degradation.