Kinetic mechanisms of electron bifurcation with electron transfer flavoprotein, NADH, butyryl-CoA dehydrogenase, and ferredoxin reveal a semiquinone cycle
Issued Date
2025-10-01
Resource Type
ISSN
00219258
eISSN
1083351X
Scopus ID
2-s2.0-105018584201
Pubmed ID
40967436
Journal Title
Journal of Biological Chemistry
Volume
301
Issue
10
Rights Holder(s)
SCOPUS
Bibliographic Citation
Journal of Biological Chemistry Vol.301 No.10 (2025)
Suggested Citation
Sucharitakul J., Mangkalee M., Intasian P., Pornsuwan S., Ermler U., Buckel W., Chaiyen P. Kinetic mechanisms of electron bifurcation with electron transfer flavoprotein, NADH, butyryl-CoA dehydrogenase, and ferredoxin reveal a semiquinone cycle. Journal of Biological Chemistry Vol.301 No.10 (2025). doi:10.1016/j.jbc.2025.110727 Retrieved from: https://repository.li.mahidol.ac.th/handle/123456789/112683
Title
Kinetic mechanisms of electron bifurcation with electron transfer flavoprotein, NADH, butyryl-CoA dehydrogenase, and ferredoxin reveal a semiquinone cycle
Corresponding Author(s)
Other Contributor(s)
Abstract
Electron transfer flavoprotein (EtfAB, with α-FAD and β-FAD) and tetrameric butyryl-CoA dehydrogenase (Bcd, with δ-FAD in each subunit) from Acidaminococcus fermentans catalyze electron bifurcation which reduces low potential ferredoxin (Fd) and high potential crotonyl-CoA using NADH as an electron donor. Our previous rapid kinetic studies have demonstrated “pseudo-electron bifurcation” where NADH and two EtfAB molecules generate EtfA<inf>SQ</inf>B (A<inf>SQ</inf> contains α-FAD<sup>•−</sup>) and the charge-transfer complex of EtfA<inf>SQ</inf>B<inf>HQ</inf>:NAD<sup>+</sup> (B<inf>HQ</inf> contains β-FADH<sup>−</sup>). Since the radical in EtfA<inf>SQ</inf>B inhibits the further reduction of β-FAD with NADH, the question arises as to how the five components of the complete system interact to mediate the whole flavin-based electron bifurcation. This study shows that Bcd releases the inhibition effect of α-FAD<sup>•−</sup>, allowing fast β-FAD reduction for turnover. In the presence of both Bcd and Fd, the total β-FADH<sup>−</sup> of EtfAB bifurcates to afford α-FAD<sup>•−</sup> and Fd<sup>−</sup>; a second bifurcation yields α-FADH<sup>−</sup> in the Bcd-EtfA<inf>HQ</inf>B complex and additional Fd<sup>−</sup>. In the presence of crotonyl-CoA, two simultaneous one-electron transfers from both EtfA<inf>HQ</inf>B yield reduced Bcd and two EtfA<inf>SQ</inf>B, confirmed by electron paramagnetic resonance spectroscopy. This step is proposed to require a slow conformational change of the Bcd-EtfAB complex for electron transfer with a limiting rate constant of 0.0098 s<sup>−1</sup> at 4 °C, but increases about 14-fold to 0.14 s<sup>−1</sup> at 30 °C, the optimal growth temperature of A. fermentans. The final reduction of crotonyl-CoA to butyryl-CoA completes the cycle, which we call the semiquinone cycle of electron bifurcation, because it starts and ends with a semiquinone.