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Dihydroorotate Dehydrogenase in Liver and Morris Hepatomas

The Lilly Research Laboratories, Eli Lilly and Company, Indianapolis, Indiana 46206

Dihydroorotate dehydrogenase (DHODH) activity in the 3683, 3924A, 7288C, and 5123D Morris hepatomas was one-half that of normal rat liver. However, the DHODH activity in Morris hepatoma 7800 was the same as that of rat liver. No correlation existed between the activities of DHODH and the rates of growth of the hepatomas.

The K_m's of the DHODH of the hepatomas ranged from 2.5 to 11.5 x 10^-5 M and were similar to the K_m's of 4.2 x 10^-5 for liver from Buffalo rats and 8.25 x 10^-5 M for liver from ACI rats. Both rat livers and the five hepatomas had a pH optimum of 8.05 ± 0.1 for DHODH The activity of DHODH from liver was not influenced by fasting, refeeding, or partial hepatectomy in Buffalo and ACI rats, except for an increase in the livers of fasting ACI rats.

Received 8/ 9/72. Accepted 11/ 3/72.