Electron transfer reaction of stellacyanin at a bare glassy carbon electrode

Abstract

Direct (unmediated) electrochemistry of Rhus verniciferu stellacyanin at a glassy carbon electrode has been briefly investigated in phosphate buffer. The voltammetry was practically independent of the buffer concentration, suggesting that the interaction between stellacyanin and the glassy carbon electrode is mainly realized through the hydrophobic interaction. The quasi-reversible process was found to be diffusion controlled at a sweep rate < 80 mVs-I. From stellacyanin concentration dependence, a transformation from linear diffusion to radial diffusion was observed. Twostep voltammetry was affected by translocations of the active site (rotation of the protein molecule on the electrode surface and diffusion). Activation energies for reduction and oxidation processes were determined to be 24kJmol-' and 54k.Tmol-l, respectively, by the stationary method, and 15 k.Tmol-' and 66 Hmol-I, respectively, by cyclic voltammetry. The considerable difference in the activation energies is supposedly due to the reduction and oxidation which are performed utilizing different electron-transfer pathways or because only one electron-transfer pathway (probably through His92) is significantly changed during the reorganization between the oxidized and reduced forms. The fact that the diffusion constant estimated from one-step voltammetry (Dox= 4.2 X10-9 cm2 s-I for 484 pM stellacyanin) is much smaller than that determined from cyclic voltammetry (7.5X10-7 cm2 s-I) derives from the fact that motions of the stellacyanin molecule (rotation leading to translocation of the active site and diffusion) are not fast enough to allow data from potential step voltammetry to be treated as the reversible process, but are fast enough to allow data from cyclic voltammetry to be treated as a diffusion-controlled process.The electron-transfer reaction has received special attention for more than fifty years, since it is involved in important biological processes such as photosynthesis and respiration [l-41. Many of the studies have focused on revealing how the electron-transfer chains are constituted by the relevant proteins, how the redox couple recognize each other, and how the intermolecular and intramolecular electron transfers take place.The rate of the biological electron-transfer processes depends on an interplay of several factors such as the distance between the donor and acceptor, their orientation with respect to each other, the nature of the intervening medium and the groups involved in the transfer pathway, the thermodynamic driving force, and atomic motions coupled with electron transfer [ 5 ] .Together with cytochromes and iron-sulfur proteins, blue copper proteins also play a role in biological electron transfers [6, 71. This type of metalloprotein contains only oneCorrespondence to

Role of the active-site cysteine of Pseudomonas aeruginosa azurin. Crystal structure analysis of the CuII(Cys112Asp) protein

“…1 gave E7(Cu II/I ) p 180 B 10 mV vs NHE (pH 7.0) [20]. Although the reduction potential of Cu II (Cys112Asp) mutant is significantly lower than that of WT azurin (310 mV vs NHE at pH 7.0) [27], it still falls within the range reported for blue proteins; in fact, the potential is the same as that of stellacyanin [28]. A decrease in reduction potential observed upon substitution of Cys112 with Asp would be expected based on the hardness of the carboxylate oxygen atoms and the change to a Cu II -stabilizing tetragonal coordination environment.…”

Structure and function of type I copper in multicopper oxidases

“…However, since the type I copper site in MCO is located under the substrate-binding cleft, the electrochemistry of MCO is unfavorable compared to blue copper protein, in which the imidazole edge of the His ligand is exposed on the flat protein surface [85][86][87][88]. In the case of NIR, the electrochemical communication of type I copper with the electrode was effectively performed by using an Au electrode modified with a promoter [89] and still more effectively by using mediator proteins such as azurin and pseudoazurin, thus affording an analytical method to measure enzyme activity [90].…”

Enzymatic Digestion and Mass Spectroscopies of N-Linked Glycans in Lacquer Stellacyanin fromRhus vernicifera

“…The LC/MS/MS spectra of trypsin-digested lacquer stellacyanin are shown in Figure 2 International Journal of Polymer Science From the observed molecular weight in Figure 2(c) and the MS/MS profile of the glycopeptides between 605.4 and 2286.7 [8], the N-linked glycan at Asn28 was characterized as (HexNAc)4(Hex)5(Fuc)3Xyl, a complex type glycan obtained from the product ion spectrum with doubly charged m/z = 1399.87. Other forms of the complex type glycans were observed in Asn28, as shown in Table 2.…”

“…These glycoproteins are plant specific glycoproteins belonging to the phytocyanin subclass of the cupredoxins. Stellacyanin is an electron transfer protein [8] and is involved in a redox process during primary defence, lignin formation, and cell-to-cell signalling transmission; however, the exact physiological function is still unclear [9][10][11]. In addition, N-linked glycans in plant glycoproteins have been shown to affect catalytic activity, thermostability, lignin formation, folding or subcellular localization, and secretion [12,13].…”