Incorporation of exogenous heme into hepatic cytochrome P-450 in vivo.

Parenteral administration of [3H]heme to allylisopropylacetamide-treated rats resulted in the formation of a radiolabeled allylisopropylacetamide-porphyrin adduct in the liver, which was isolated and purified. Since formation of this adduct requires the heme moiety of a functional cytochrome P-450 species, our findings indicate that exogenously supplied heme had been incorporated into the hepatic microsomal hemoprotein. Moreover, they suggest that exogenously supplied heme readily gains access to an "unassigned" heme pool, which provides heme for cytochrome P-450 formation.