Tetralin as a Substrate for Camphor (Cytochrome P450) 5-Monooxygenase

Camphor (cytochrome P450) 5-monooxygenase, originally isolated from the bacteriumPseudomonas putidaPgG 786, catalyzes the essentially stereospecific conversion of tetralin (1,2,3,4-tetrahydronaphthalene) to (R)-1-tetralol ((R)-(−)-1,2,3,4-tetrahydro-1-naphthol): tetralin(aq) + NADH(aq) + O2(aq) = (R)-1-tetralol(aq) + NAD(aq) + H2O(l). The ratio of the amount of (S)-1-tetralol to the amount of (R)-1-tetralol is small (≈0.04) and the reaction is essentially stereospecific. The reaction time–course plot indicates the formation of additional product(s) from the (R)-1-tetralol. It is found that the above reaction obeys Michaelis–Menten kinetics and that dimethyl sulfoxide, methanol, andp-dioxane serve as accelerators. Approximate values of a Michaelis constantKm, limiting rateVmax, and catalytic constantkcatare obtained for this reaction under a specified set of conditions. It is shown by means of a thermochemical cycle calculation that the apparent equilibrium constant for this reaction is ≈4 × 1065atT= 298.15 K and pH 7.3. Thus, this reaction is “irreversible” and, unless the enzyme system is inactivated, it will proceed in the direction of complete formation of 1-tetralol from tetralin. A detailed description of the preparation of the camphor (cytochrome P450) 5-monooxygenase enzyme system from recombinant microorganisms is given.