Biophysical and catalytic properties of the phenobarbital p-hydroxylase--a cytochrome P-450 dependent mixed function oxidase.

1. A sensitive method to detect and quantify the products of phenobarbital (PB) hydroxylation by model chemical systems and by biological systems has been developed. 2. Chemical model systems hydroxylate PB in the p-position of the phenyl ring and form one or two additional oxidation products, while in vitro and in vivo (bile fistula rats) biological systems hydroxylate PB only in the p-position. 3. Phenobarbital hydroxylation rates in vitro are of the order of 0.007 nmol/nmol cytochrome P-450 per min. These values are decreased by pretreatment of the rats with inducing doses of phenobarbital. 4. Enzymes catalysing the p-hydroxylation reaction of phenobarbital are localized in the microsomes and have the biophysical and chemical properties that are usually associated with cytochrome P-450-dependent mixed function oxidases.