Substrate Specificity of Soluble Methane Monooxygenase

ion or by sequential loss of a *-bond electron and a proton termed an aborted epoxidation by Ortiz de Montellano (1986) and indeed epoxidated products are generated by methane monooxygenase from these substrates (Table 111). Oxidation of Cyclopropylbenzem-Attaching a cyclopropyl ring to the hydroxylated carbon atom of a hydrocarbon substrate as a means of testing for the presence of carbon radical intermediates in an oxidation has been widely applied (Ortiz de Montellano, 1986; Jezequel, 1986; Dalton et al., 1981). This approach, based on the rapid rearrangement of cyclopropylmethyl to 3-butenyl radicals, failed to yield any ring-opened products when used previously with methane monooxygenase preparations utilizing cyclopropylmethane as substrate (Dalton et al., 1981). Jezequel (1986) found the methane monooxygenase from M. trichosporium OB3b did yield ring-opened products from cyclopropylphenylmethane (30% of the product was 4-phenylbut-2-ene-1-01). Using cyclopropylbenzene as substrate with purified methane monooxygenase from M. capsulatus (Bath) we have identified a ring-opened product in 3-phenylprop-2-en-1-01 as well as 4-cyclopropylphenol and benzyl alcohol (Table IV). The observation of ring-opened products in the aromatic cyclopropane derivatives may have been due to the greater strain imposed upon the cyclopropane ring which would tend to accelerate ring opening. Thus the opening of the cyclopropyl ring implies the presence of a nonconcerted oxidation mechanism with a charged or radical intermediate. The production of benzyl alcohol compares with 17700 Mechanism of Methane Monooxygenase