N-oxidation of phentermine to N-hydroxyphentermine by a reconstituted cytochrome P-450 oxidase system from rabbit liver.

Previous studies in our laboratory have indicated that the cytochrome P-450 system is involved in the oxidation of phentermine (2-methyl-1-phenyl-2-aminopropane) to N-hydroxyphentermine by liver microsomal preparations. In the present study, a reconstituted system which consisted of cytochrome P-450 and NADPH cytochrome P-450 reductase purified from liver microsomes of phenobarbital-induced rabbits was found to oxidize phentermine to N-hydroxyphentermine. The reaction was NADPH-dependent and required the presence of both the cytochrome P-450 and reductase preparations. N-Hydroxyphentermine was formed 3 times more rapidly in incubation mixtures which contained dilauroyl phosphatidylcholine than in those without added phospholipid. The reaction was inhibited several-fold by octylamine. It is concluded that the cytochrome P-450 system is able to catalyze the oxidation of phentermine to N-hydroxyphentermine.