Direct electron transfer from graphite and functionalized gold electrodes to T1 and T2/T3 copper centers of bilirubin oxidase.
Direct electron transfer (DET) from bare spectrographic graphite (SPGE) or 3-mercaptopropionic acid-modified gold (MPA-gold) electrodes to Trachyderma tsunodae bilirubin oxidase (BOD) was studied under anaerobic and aerobic conditions by cyclic voltammetry and chronoamperometry. On cyclic voltammograms nonturnover Faradaic signals with midpoint potentials of about 700 mV and 400 mV were clearly observed corresponding to redox transformations of the T1 site and the T2/T3 cluster of the enzyme, respectively. The immobilized BOD was differently oriented on the two electrodes and its catalysis of O(2)-electroreduction was also massively different. On SPGE, where most of the enzyme was oriented with the T1 copper site proximal to the carbon with a quite slow ET process, well-pronounced DET-bioelectroreduction of O(2) was observed, starting already at >700 mV vs. NHE. In contrast, on MPA-gold most of the enzyme was oriented with its T2/T3 copper cluster proximal to the metal. Indeed, there was little DET-based catalysis of O(2)-electroreduction, even though the ET between the MPA-gold and the T2/T3 copper cluster of BOD was similar to that observed for the T1 site at SPGE. When BOD actively catalyzes the O(2)-electroreduction, the redox potential of its T1 site is 690 mV vs. NHE and that of one of its T2/T3 copper centers is 390 mV vs. NHE. The redox potential of the T2/T3 copper cluster of a resting form of BOD is suggested to be about 360 mV vs. NHE. These values, combined with the observed biocatalytic behavior, strongly suggest an uphill intra-molecular electron transfer from the T1 site to the T2/T3 cluster during the catalytic turnover of the enzyme.
Ramírez
Pablo
P
Departamento de Química Física, Universidad de Sevilla, Sevilla, Spain.
Mano
Nicolas
N
Andreu
Rafael
R
Ruzgas
Tautgirdas
T
Heller
Adam
A
Gorton
Lo
L
Shleev
Sergey
S
D015097:3-Mercaptopropionic Acid / Q000737:chemistry; D000327:Adsorption; D003300:Copper / Q000737:chemistry*; D004563:Electrochemistry; D004566:Electrodes; D004579:Electron Transport; D005656:Fungal Proteins / Q000737:chemistry; D006046:Gold / Q000737:chemistry*; D006108:Graphite / Q000737:chemistry*; D010084:Oxidation-Reduction; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000737:chemistry*; D013499:Surface Properties
D005656:Fungal Proteins; D006046:Gold; D006108:Graphite; D003300:Copper; D015097:3-Mercaptopropionic Acid; D044925:Oxidoreductases Acting on CH-CH Group Donors; C042401:bilirubin oxidase