Abstract

The addition of increasing concentrations of a detergent (Triton X-100)-solubilized cytochrome b₅ from liver microsomes to liver microsomes of untreated or phenobarbital-treated animals produced correspondingly greater inhibition of aminopyrine dealkylation. Even addition of NADH to the NADPH-supported reaction did not prevent this inhibition, although the added cytochrome b₅ functioned as an endogenous hemoprotein; i.e., it was reduced by NADH and stimulated the reduction of exogenous cytochrome c. These observations suggest that cytochrome b₅ does not function in hepatic microsomal mixedfunction oxidase reactions.