title: Multiple roles of component proteins in bacterial multicomponent monooxygenases: phenol hydroxylase and toluene/o-xylene monooxygenase from Pseudomonas sp. OX1.
abstract: Phenol hydroxylase (PH) and toluene/o-xylene monooxygenase (ToMO) from Pseudomonas sp. OX1 require three or four protein components to activate dioxygen for the oxidation of aromatic substrates at a carboxylate-bridged diiron center. In this study, we investigated the influence of the hydroxylases, regulatory proteins, and electron-transfer components of these systems on substrate (phenol; NADH) consumption and product (catechol; H(2)O(2)) generation. Single-turnover experiments revealed that only complete systems containing all three or four protein components are capable of oxidizing phenol, a major substrate for both enzymes. Under ideal conditions, the hydroxylated product yield was ∼50% of the diiron centers for both systems, suggesting that these enzymes operate by half-sites reactivity mechanisms. Single-turnover studies indicated that the PH and ToMO electron-transfer components exert regulatory effects on substrate oxidation processes taking place at the hydroxylase actives sites, most likely through allostery. Steady state NADH consumption assays showed that the regulatory proteins facilitate the electron-transfer step in the hydrocarbon oxidation cycle in the absence of phenol. Under these conditions, electron consumption is coupled to H(2)O(2) formation in a hydroxylase-dependent manner. Mechanistic implications of these results are discussed.
authors.affiliation: Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
authors.forename: Christine E
authors.initials: CE
authors.lastname: Tinberg
authors.forename: Woon Ju
authors.initials: WJ
authors.lastname: Song
authors.forename: Viviana
authors.initials: V
authors.lastname: Izzo
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Lippard
mesh_terms: D001665:Binding Sites; D002396:Catechols / Q000378:metabolism; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D009243:NAD / Q000737:chemistry / Q000378:metabolism; D010084:Oxidation-Reduction; D010105:Oxygenases / Q000737:chemistry* / Q000378:metabolism*; D019800:Phenol / Q000378:metabolism; D011487:Protein Conformation; D011549:Pseudomonas / Q000201:enzymology* / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D002396:Catechols; D009243:NAD; D019800:Phenol; D006899:Mixed Function Oxygenases; D010105:Oxygenases; C114360:toluene 2-xylene monooxygenase; C022336:phenol 2-monooxygenase