The catalytic reaction of copper amine oxidase proceeds through a ping-pong mechanism comprising two half-reactions. In the initial half-reaction, the substrate amine reduces the Tyr-derived cofactor, topa quinone (TPQ), to an aminoresorcinol form (TPQamr) that is in equilibrium with a semiquinone radical (TPQsq) via an intramolecular electron transfer to the active-site copper. We have analyzed this reductive half-reaction in crystals of the copper amine oxidase from Arthrobacter globiformis. Anerobic soaking of the crystals with an amine substrate shifted the equilibrium toward TPQsq in an "on-copper" conformation, in which the 4-OH group ligated axially to the copper center, which was probably reduced to Cu(I). When the crystals were soaked with substrate in the presence of halide ions, which act as uncompetitive and noncompetitive inhibitors with respect to the amine substrate and dioxygen, respectively, the equilibrium in the crystals shifted toward the "off-copper" conformation of TPQamr. The halide ion was bound to the axial position of the copper center, thereby preventing TPQamr from adopting the on-copper conformation. Furthermore, transient kinetic analyses in the presence of viscogen (glycerol) revealed that only the rate constant in the step of TPQamr/TPQsq interconversion is markedly affected by the viscogen, which probably perturbs the conformational change. These findings unequivocally demonstrate that TPQ undergoes large conformational changes during the reductive half-reaction.
The N-glycosylation in pea seedling amine oxidase and lentil seedling amine oxidase was analyzed in the present work. For that purpose, the enzymes were purified as native proteins from their natural sources. An enzymatic deglycosylation of pea seedling amine oxidase by endoglycosidase H under denaturing conditions combined with its proteolytic digestion by trypsin was carried out in order to analyze both N-glycans and "trimmed" N-glycopeptides with a residual N-acetylglucosamine attached at the originally occupied N-glycosylation sites. The released N-glycans were subjected to a manual chromatographic purification followed by MALDI-TOF/TOF MS. MS and MS/MS analyses were also performed directly on peptides and N-glycopeptides generated by proteolytic digestion of the studied enzymes. Sequencing of glycopeptides by MALDI-TOF/TOF MS/MS after their separation on a RP using a microgradient chromatographic device clearly demonstrated binding of paucimannose and hybrid N-glycan structures at Asn558. Such carbohydrates have been reported to exist in many plant N-glycoproteins, e.g. in peroxidases. Although high-mannose glycan structures were identified after the enzymatic deglycosylation, they could not be assigned to a particular N-glycosylation site. The presence of unoccupied glycosylation sites in several peptides was also confirmed from MS/MS results.
- MeSH
- glykopeptidy analýza chemie izolace a purifikace MeSH
- glykosylace MeSH
- histaminasa analýza chemie metabolismus MeSH
- Lathyrus chemie enzymologie MeSH
- mannosyl-glykoprotein endo-beta-N-acetylglukosaminidasa chemie MeSH
- molekulární modely MeSH
- molekulární sekvence - údaje MeSH
- polysacharidy analýza chemie izolace a purifikace MeSH
- rostlinné proteiny analýza chemie metabolismus MeSH
- sekvence aminokyselin MeSH
- sekvenční seřazení MeSH
- spektrometrie hmotnostní - ionizace laserem za účasti matrice metody MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- MeSH
- adenin analogy a deriváty chemie MeSH
- cytokiny chemie metabolismus MeSH
- dihydroxyfenylalanin analogy a deriváty farmakologie MeSH
- finanční podpora výzkumu jako téma MeSH
- histaminasa farmakologie chemie MeSH
- inhibitory enzymů farmakologie MeSH
- léčivé rostliny metabolismus MeSH
- rostlinné extrakty MeSH
- rostliny metabolismus MeSH
