Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2010 Dec;1797(12):1891-3.
doi: 10.1016/j.bbabio.2010.06.010. Epub 2010 Jun 25.

Possible roles of two quinone molecules in direct and indirect proton pumps of bovine heart NADH-quinone oxidoreductase (complex I)

S Tsuyoshi Ohnishi  1 , John C Salerno, Tomoko Ohnishi
Affiliations

Possible roles of two quinone molecules in direct and indirect proton pumps of bovine heart NADH-quinone oxidoreductase (complex I)

S Tsuyoshi Ohnishi et al. Biochim Biophys Acta. 2010 Dec.

Abstract

In many energy transducing systems which couple electron and proton transport, for example, bacterial photosynthetic reaction center, cytochrome bc(1)-complex (complex III) and E. coli quinol oxidase (cytochrome bo(3) complex), two protein-associated quinone molecules are known to work together. T. Ohnishi and her collaborators reported that two distinct semiquinone species also play important roles in NADH-ubiquinone oxidoreductase (complex I). They were called SQ(Nf) (fast relaxing semiquinone) and SQ(Ns) (slow relaxing semiquinone). It was proposed that Q(Nf) serves as a "direct" proton carrier in the semiquinone-gated proton pump (Ohnishi and Salerno, FEBS Letters 579 (2005) 4555), while Q(Ns) works as a converter between one-electron and two-electron transport processes. This communication presents a revised hypothesis in which Q(Nf) plays a role in a "direct" redox-driven proton pump, while Q(Ns) triggers an "indirect" conformation-driven proton pump. Q(Nf) and Q(Ns) together serve as (1e(-)/2e(-)) converter, for the transfer of reducing equivalent to the Q-pool.

PubMed Disclaimer

Figures

Fig. 1
Fig. 1
A scheme is to show the flows of electrons and protons in bovine heart complex I. Aarrows of direct pump and indirect pump indicate that these two pumps are driven by two kinds of ubiquinone species. At the end of the cycle, bc1 indicates the coupling to complex III via Qpool.
Fig. 2
Fig. 2
Schematic mechanisms of the (a)-(c) QNf-gated “direct” proton pump which transports 2 protons, and (d)-(f) QNs-induced conformation-driven “indirect” proton pump which also transports 2 protons.
See this image and copyright information in PMC

References

    1. Adelroth P, Paddock ML, Sagle LB, Feher G, Okamura MY. Identification of the proton pathway in bacterial reaction centers: both protons associated with reduction of QB to QBH2 share a common entry point. Proc Natl Acad Sci U S A. 2000;97:13086–13091. - PMC - PubMed
    1. Okamura MY, Paddock ML, Graige MS, Feher G. Proton and electron transfer in bacterial reaction centers. Biochim Biophys Acta. 2000;1458:148–163. - PubMed
    1. Mitchell P. Protonmotive redox mechanism of the cytochrome b-c1 complex in the respiratory chain: protonmotive ubiquinone cycle. FEBS Lett. 1975;56:1–6. - PubMed
    1. Croft AR. The cytochrome bc1 complex: Function in the context of structure. Annu. Rev. Physiol. 2004;66:689–733. - PubMed
    1. Sato-Watanabe M, Mogi T, Ogura T, Kitagawa T, Miyoshi H, Iwamura H, Anraku Y. Identification of a novel quinone-binding site in the cytochrome bo complex from Escherichia coli. J Biol Chem. 1994;269:28908–28912. - PubMed

Publication types

LinkOut - more resources