title: Comparison of the characteristics of fungal and plant tyrosinases.
abstract: Enzymatic crosslinking provides valuable means for modifying functionality and structural properties of different polymers. Tyrosinases catalyze the hydroxylation of various monophenols to the corresponding o-diphenols, and the subsequent oxidation of o-diphenols to the corresponding quinones, which are highly reactive and can further undergo non-enzymatic reactions to produce mixed melanins and heterogeneous polymers. Tyrosinases are also capable of oxidizing protein- and peptide-bound tyrosyl residues, resulting in the formation of inter- and intra-molecular crosslinks. Tyrosinases from apple (AT), potato (PT), the white rot fungus Pycnoporus sanguineus (PsT), the filamentous fungus Trichoderma reesei (TrT) and the edible mushroom Agaricus bisporus (AbT) were compared for their biochemical characteristics. The enzymes showed different features in terms of substrate specificity, stereo-specificity, inhibition, and ability to crosslink the model protein, alpha-casein. All enzymes were found to produce identical semiquinone radicals from the substrates as analyzed by electron spin resonance spectroscopy. The result suggests similar reaction mechanism between the tyrosinases. PsT enzyme had the highest monophenolase/diphenolase ratio for the oxidation of monophenolic L-tyrosine and diphenolic L-dopa, although the tyrosinases generally had noticeably lower activity on monophenols than on di- or triphenols. The activity of AT and PT on tyrosine was particularly low, which largely explains the poor crosslinking ability of the model protein alpha-casein by these enzymes. AbT oxidized peptide-bound tyrosine, but was not able to crosslink alpha-casein. Conversely, the activity of PsT on model peptides was relatively low, although the enzyme could crosslink alpha-casein. In the reaction conditions studied, TrT showed the best ability to crosslink alpha-casein. TrT also had the highest activity on most of the tested monophenols, and showed noticeable short lag periods prior to the oxidation.
authors.affiliation: VTT Technical Research Centre of Finland, P.O. Box 1000, Espoo FIN-02044 VTT, Finland.
authors.forename: Emilia
authors.initials: E
authors.lastname: Selinheimo
authors.forename: Deirdre
authors.initials: D
authors.lastname: NiEidhin
authors.forename: Charlotte
authors.initials: C
authors.lastname: Steffensen
authors.forename: Jacob
authors.initials: J
authors.lastname: Nielsen
authors.forename: Anne
authors.initials: A
authors.lastname: Lomascolo
authors.forename: Sonia
authors.initials: S
authors.lastname: Halaouli
authors.forename: Eric
authors.initials: E
authors.lastname: Record
authors.forename: David
authors.initials: D
authors.lastname: O'Beirne
authors.forename: Johanna
authors.initials: J
authors.lastname: Buchert
authors.forename: Kristiina
authors.initials: K
authors.lastname: Kruus
mesh_terms: D004789:Enzyme Activation; D004795:Enzyme Stability; D005656:Fungal Proteins / Q000737:chemistry*; D005658:Fungi / Q000201:enzymology*; D014442:Monophenol Monooxygenase / Q000737:chemistry*; D010940:Plant Proteins / Q000737:chemistry*; D010944:Plants / Q000201:enzymology*; D013379:Substrate Specificity
chemical_list: D005656:Fungal Proteins; D010940:Plant Proteins; D014442:Monophenol Monooxygenase