Aromatic Hydroxylation Catalyzed by Toluene 4-Monooxygenase in Organic Solvent/Aqueous Buffer Mixtures

摘要

Toluene 4-monooxygenase is a four-protein component diiron enzyme complex. The enzyme catalyzes the hydroxylation of toluene to give p-cresol with -96% regioselectivity .The performance of the enzyme in two-phase reaction systems consisting of toluene, hexane, or perfluorohexane and an aqueous buffer was tested. In each of the cosolvent systems, containing up to 93% (v iv) of solvent, the enzyme was active and exhibited regioselectivity indistinguishable from the aqueous reaction. Using the perfluorohexanei buffer system, a number of polycyclic aromatic hydrocarbons were oxidized that were not readily oxidized in aqueous buffer. An instability of the hydroxylase component and a substantial uncoupling of NADH utilization and product formation were observed in reactions that were continued for longer than -3 min. More stable enzyme complexes will be needed for broad applicability of this hydroxylating system in nonaqueous media.