Mechanistic Studies on Non-Heme Iron Monooxygenase Catalysis: Epoxidation, Aldehyde Formation, and Demethylation by the ω-Hydroxylation System of Pseudomonas oleovorans

Article abstract of DOI:10.1021/ja00337a049

In previous work we have established that the "ω-hydroxylation" system of P. oleovorans readily converts terminal olefins to the corresponding 1,2-oxides and does so stereoselectively.We also demonstrated loss of olefin configuration during enzymatic epoxidation, a result inconsistent with a concerted epoxidation mechanism (J.Am.Chem.Soc. 1977, 99, 2017-2024).Since loss of olefin configuration is unprecedented for monooxygenase-catalyzed epoxidations these studies have been confirmed with isolated enzymes and further extended in order to probe the mechanism of non-heme iron monooxygenase catalysis.Enzymatic epoxidation of both cis- and trans-1-deuterio-1-octene proceeds with about 70percent inversion of the olefinic configuration, with corresponding results being obtained for the two olefins.As we reported in a preliminary communication (Bio/Technology 1983, 1, 677-686, the ω-hydroxylation system also produces aldehydes from olefins.Aldehyde formations exhibits the reaction characteristics expected for the usual oxygenase pathway.Deuterium migration from C-1 to C-2 occurs in formation of aldehyde from olefin, although loss of deuterium also occurs.The ω-hydroxylation system was found to efficiently catalyze O-demethylation of heptyl methyl ether, the first demonstration of such activity for a non-heme iron monooxygenase of this type.Taken together, the results provide support for a two-step mechanism involving enzyme generated species with cationic and/or radical character, which accounts for the stereoselectivity, configurational loss, substrate specificity, formation of aldehydes with deuterium migration, and demethylation activity exhibited by this enzyme system.