Transformation of ortho-substituted biphenyls by Methylosinus trichosporium OB3b: substituent effects on oxidation kinetics and product formation

The ability of Methylosinus trichosporium OB3b, expressing soluble methane monooxygenase, to oxidize a range of ol-tho-substituted biphenyls was exami ned to better understand how substituents affect both the rate and products of oxidation in comparison to biphenyl. Inhibition of oxidation was observ ed over the tested substrate range for both biphenyl and ortho-halogenated biphenyls (2-chloro-, 2-bromo-, and 2-iodobiphenyl), No inhibition was obse rved during the oxidation of 2-hydroxybiphenyl and 2-methylbiphenyl. Analys is of the products of oxidation showed that, depending on the substituent, ring hydroxylation, substituent oxidation, and elimination pathways could o ccur. The type and abundance of products formed along with the relatively h igh kinetic isotope effect observed for deuterated vs. nondeuterated biphen yl (k(h)/k(d) = 3.4 +/- 0.02) are consistent with mechanisms that include b oth hydrogen abstraction and NIH-shift pathways. Knowledge of these substit uent-dependent reaction rates and mechanisms enhances our understanding of the methanotrophic aryl transformation potential and allows for better pred iction of the formation of oxidized intermediates by methanotrophic bacteri a.