title: C(sp3)-H bond hydroxylation catalyzed by myoglobin reconstituted with manganese porphycene.
abstract: Myoglobin reconstituted with manganese porphycene was prepared in an effort to generate a new biocatalyst and was characterized by spectroscopic techniques. The X-ray crystal structure of the reconstituted protein reveals that the artificial cofactor is located in the intrinsic heme-binding site with weak ligation by His93. Interestingly, the reconstituted protein catalyzes the H2O2-dependent hydroxylation of ethylbenzene to yield 1-phenylethanol as a single product with a turnover number of 13 at 25 °C and pH 8.5. Native myoglobin and other modified myoglobins do not catalyze C-H hydroxylation of alkanes. Isotope effect experiments yield KIE values of 2.4 and 6.1 for ethylbenzene and toluene, respectively. Kinetic data, log kobs versus BDE(C(sp(3))-H) for ethylbenzene, toluene, and cyclohexane, indicate a linear relationship with a negative slope. These findings clearly indicate that the reaction occurs via a rate-determining step that involves hydrogen-atom abstraction by a Mn(O) species and a subsequent rebound hydroxylation process which is similar to the reaction mechanism of cytochrome P450.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Osaka University , Suita, 565-0871, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Oohora
authors.forename: Yushi
authors.initials: Y
authors.lastname: Kihira
authors.forename: Eiichi
authors.initials: E
authors.lastname: Mizohata
authors.forename: Tsuyoshi
authors.initials: T
authors.lastname: Inoue
authors.forename: Takashi
authors.initials: T
authors.lastname: Hayashi
mesh_terms: D000473:Alkanes / Q000737:chemistry / Q000378:metabolism*; D055162:Biocatalysis; D018360:Crystallography, X-Ray; D006861:Hydrogen Peroxide / Q000737:chemistry / Q000378:metabolism; D006900:Hydroxylation; D008345:Manganese / Q000737:chemistry*; D008665:Metalloporphyrins / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D015394:Molecular Structure; D009211:Myoglobin / Q000737:chemistry / Q000378:metabolism*; D009942:Organometallic Compounds / Q000737:chemistry / Q000378:metabolism
chemical_list: D000473:Alkanes; D008665:Metalloporphyrins; D009211:Myoglobin; D009942:Organometallic Compounds; D008345:Manganese; D006861:Hydrogen Peroxide