[Activity of key enzymes of heme synthesis and degradation and contents of cytochromes b5 and P-450 in rat liver].

The relation between the delta-aminolevulinate-synthase and heme-oxygenase activities and the contents of cytochromes b5 and P-450 in rat liver after phenobarbital and CoCl2 injections was studied. Two hours after a single injection of phenobarbital the delta-aminolevulinate-synthase activity is increased, showing a further rise after 24 hrs. The content of cytochrome b5 is not changed, while that of cytochrome P-450 is increased 24 hrs after the injection. The heme-oxygenase activity remains unaffected thereby. The increase in the enzyme activity and cytochrome P-450 content induced by phenobarbital is eliminated by a preliminary administration of actinomycin D. The administration of CoCl2 is accompanied by a decrease in the delta-aminolevulinate-synthase activity after 2 hrs and its further increase after 24 hrs. The heme-oxygenase activity shows a sharp rise 24 hrs after the injection. The rise in the delta-aminolevulinate-synthase activity induced by CoCl2 is removed by actinomycin D. CoCl2 decreases the content of cytochromes b5 and P-450 24 hrs after the injection. It is assumed that the correlation between the delta-aminolevulinate-synthase activity and cytochrome P-450 content is observed only in the case when the heme-oxygenase activity is not increased. The cytochrome b5 content is independent of the changes in the activity of the key enzyme of heme synthesis and depends to a certain extent on the rate of heme degradation by heme-oxygenase.