TY - JOUR
T1 - Proton-coupled electron transfer mechanisms of the copper centres of nitrous oxide reductase from Marinobacter hydrocarbonoclasticus – An electrochemical study
AU - Carreira, Cíntia
AU - dos Santos, Margarida M. C.
AU - Pauleta, Sofia R.
AU - Moura, Isabel
N1 - info:eu-repo/grantAgreement/FCT/SFRH/SFRH%2FBD%2F87898%2F2012/PT #
PTDC/BBB-BQB/0129/2014,
FCT/MCTES, UID/Multi/04378/2019,
UID/QUI/50006/2019,
Centro de Quimica Estrutural multiannual funding 2020-2023,
UID/QUI/00100/2019.
PY - 2020/6/1
Y1 - 2020/6/1
N2 - Reduction of N2O to N2 is catalysed by nitrous oxide reductase in the last step of the denitrification pathway. This multicopper enzyme has an electron transferring centre, CuA, and a tetranuclear copper-sulfide catalytic centre, “CuZ”, which exists as CuZ*(4Cu1S) or CuZ(4Cu2S). The redox behaviour of these metal centres in Marinobacter hydrocarbonoclasticus nitrous oxide reductase was investigated by potentiometry and for the first time by direct electrochemistry. The reduction potential of CuA and CuZ(4Cu2S) was estimated by potentiometry to be +275 ± 5 mV and +65 ± 5 mV vs SHE, respectively, at pH 7.6. A proton-coupled electron transfer mechanism governs CuZ(4Cu2S) reduction potential, due to the protonation/deprotonation of Lys397 with a pKox of 6.0 ± 0.1 and a pKred of 9.2 ± 0.1. The reduction potential of CuA, in enzyme samples with CuZ*(4Cu1S), is controlled by protonation of the coordinating histidine residues in a two-proton coupled electron transfer process. In the cyclic voltammograms, two redox pairs were identified corresponding to CuA and CuZ(4Cu2S), with no additional signals being detected that could be attributed to CuZ*(4Cu1S). However, an enhanced cathodic signal for the activated enzyme was observed under turnover conditions, which is explained by the binding of nitrous oxide to CuZ0(4Cu1S), an intermediate species in the catalytic cycle.
AB - Reduction of N2O to N2 is catalysed by nitrous oxide reductase in the last step of the denitrification pathway. This multicopper enzyme has an electron transferring centre, CuA, and a tetranuclear copper-sulfide catalytic centre, “CuZ”, which exists as CuZ*(4Cu1S) or CuZ(4Cu2S). The redox behaviour of these metal centres in Marinobacter hydrocarbonoclasticus nitrous oxide reductase was investigated by potentiometry and for the first time by direct electrochemistry. The reduction potential of CuA and CuZ(4Cu2S) was estimated by potentiometry to be +275 ± 5 mV and +65 ± 5 mV vs SHE, respectively, at pH 7.6. A proton-coupled electron transfer mechanism governs CuZ(4Cu2S) reduction potential, due to the protonation/deprotonation of Lys397 with a pKox of 6.0 ± 0.1 and a pKred of 9.2 ± 0.1. The reduction potential of CuA, in enzyme samples with CuZ*(4Cu1S), is controlled by protonation of the coordinating histidine residues in a two-proton coupled electron transfer process. In the cyclic voltammograms, two redox pairs were identified corresponding to CuA and CuZ(4Cu2S), with no additional signals being detected that could be attributed to CuZ*(4Cu1S). However, an enhanced cathodic signal for the activated enzyme was observed under turnover conditions, which is explained by the binding of nitrous oxide to CuZ0(4Cu1S), an intermediate species in the catalytic cycle.
KW - CuA centre
KW - CuZ centre
KW - Direct electrochemistry
KW - Nitrous oxide reductase
KW - Potentiometry
KW - Proton-coupled electron transfer
UR - http://www.scopus.com/inward/record.url?scp=85080089555&partnerID=8YFLogxK
U2 - 10.1016/j.bioelechem.2020.107483
DO - 10.1016/j.bioelechem.2020.107483
M3 - Article
C2 - 32120320
AN - SCOPUS:85080089555
SN - 1567-5394
VL - 133
JO - Bioelectrochemistry
JF - Bioelectrochemistry
M1 - 107483
ER -