title: Intramolecular electron transfer in laccases.
abstract: Rate constants and activation parameters have been determined for the internal electron transfer from type 1 (T1) to type 3 (T3) copper ions in laccase from both the fungus Trametes hirsuta and the lacquer tree Rhus vernicifera, using the pulse radiolysis method. The rate constant at 298 K and the enthalpy and entropy of activation were 25 ± 1 s(-1), 39.7 ± 5.0 kJ·mol(-1) and -87 ± 9 J·mol(-1) ·K(-1) for the fungal enzyme and 1.1 ± 0.1 s(-1), 9.8 ± 0.2 kJ·mol(-1) and -211 ± 3 J·mol(-1) ·K(-1) for the tree enzyme. The initial reduction of the T1 site by pulse radiolytically produced radicals was direct in the case of T. hirsuta laccase, but occured indirectly via a disulfide radical in R. vernicifera. The equilibrium constant that characterizes the electron transfer from T1 to T3 copper ions was 0.4 for T. hirsuta laccase and 1.5 for R. vernicifera laccase, leading to full reduction of the T1 site occurring at 2.9 ± 0.2 electron equivalents for T. hirsuta and 4 electron equivalents for R. vernicifera laccase. These results were compared with each other and with those for the same process in other multicopper oxidases, ascorbate oxidase and Streptomyces coelicolor laccase, using available structural information and electron transfer theory.
authors.affiliation: Institute of Analytical Chemistry, University of Copenhagen, Copenhagen, Denmark. of@farma.ku.dk
authors.forename: Ole
authors.initials: O
authors.lastname: Farver
authors.forename: Scot
authors.initials: S
authors.lastname: Wherland
authors.forename: Olga
authors.initials: O
authors.lastname: Koroleva
authors.forename: Dmitry S
authors.initials: DS
authors.lastname: Loginov
authors.forename: Israel
authors.initials: I
authors.lastname: Pecht
mesh_terms: D055162:Biocatalysis; D002245:Carbon Dioxide / Q000737:chemistry; D020134:Catalytic Domain; D003300:Copper / Q000737:chemistry*; D030562:Databases, Protein; D004579:Electron Transport; D019277:Entropy; D005609:Free Radicals / Q000737:chemistry; D005656:Fungal Proteins / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D042845:Laccase / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D010084:Oxidation-Reduction; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D011675:Pulse Radiolysis; D029045:Rhus / Q000201:enzymology; D055454:Trametes / Q000201:enzymology
chemical_list: D005609:Free Radicals; D005656:Fungal Proteins; D010940:Plant Proteins; D002245:Carbon Dioxide; C041069:carboxyl radical; D003300:Copper; D042845:Laccase