Abstract
Some drugs which provoke hepatomegaly or hepatic injury, were tested for their effects on the FMN and FAD-synthesizing activities in the liver of male rats. Flavokinase and FAD pyrophosphorylase activities were found to be decreased by carbon tetrachloride or ethionine; whereas phenobarbital which induces drug metabolizing enzymes, increased the activities of both flavokinase and FAD pyrophosphorylase in the liver with increasing concentrations of the drugs. On the other hand, 3-methylcholanthrene, one of the carcinogenic polycyclic hydrocarbons, which was known to induce only some specific drug metabolizing activities, showed no significant enhancement in activities of these two enzymes. Phenobarbital elicited no longer distinct induction of the activities of flavokinase and FAD pyrophosphorylase in the vitamin B_2-deficient rat. These results indicate that induction of drug metabolizing flavin enzyme activities by phenobarbital might cause not only the increment of the flavin enzyme apo-proteins, but also increase the activities of FMN and FAD synthesizing enzymes.
