Quinone reduction sites and the role of heme in succinate:quinone reductase. Studies in Bacillus subtilis and Paracoccus denitrificans

Research output: ThesisDoctoral Thesis (compilation)


Succinate:quinone reductase (SQR) is an enzyme in the respiratory system of aerobic cells. SQR catalyzes two reactions, the oxidation of succinate to fumarate and the reduction of quinone to quinol. These reactions are coupled by electron transfer within the enzyme from the site of succinate oxidation to the site of quinone reduction. Some enzymes reduce ubiquinone (exergonic reaction) whereas others reduce menaquinone (endergonic reaction). SQR is composed of one membrane-peripheral domain and one membrane-anchor domain. Succinate is oxidized on the peripheral domain which is attached to the electronegative side of the respiratory membrane. This domain consists of two polypeptides, one covalently bound FAD group, one [2Fe-2S] cluster, one [4Fe-4S] cluster and one [3Fe-4S] cluster. The anchor domain harbors the quinone reduction site(s) and is, depending on the organism, composed of one or two polypeptides and one or two b-type hemes. Succinate:menaquinone reductases contain two heme groups, one proximal heme (heme bP) located close to the negative side of the membrane and one distal heme (heme bD) located close to the positive side of the membrane. Succinate:ubiquinone reductases contain only heme bP. Electron transfer from succinate to quinone occurs in a linear pathway including the FAD, the [2Fe-2S] cluster, the [4Fe-4S] cluster, the [3Fe-4S] cluster and sometimes heme as electron carriers in the given order.

I have studied SQR from two evolutionary very distant bacteria, Bacillus subtilis and Paracoccus denitrificans. B. subtilis SQR reduces menaquinone whereas P. denitrificans SQR reduces ubiquinone. The combined experimental results support the following model. In succinate:ubiquinone reductases the quinone reduction site is located close to the [3Fe-4S] cluster on the negative side of the membrane. Heme is not required as an electron carrier in these enzymes. Ubiquinone reduction by succinate is not dependent on the transmembrane electrochemical potential. In succinate:menaquinone reductases the quinone reduction site is located close to the positive side of the membrane. Heme bP and heme bD mediate transmembrane electron transfer from the [3Fe-4S] cluster to menaquinone. The transmembrane electrochemical potential provides driving force for the endergonic reduction of menaquinone by succinate.


  • Mikael Matsson
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Biological Sciences


  • carboxin, cytochrome b, electron transport, heme, quinone, Paracoccus denitrificans, Bacillus subtilis, Succinate:quinone reductase, succinate dehydrogenase, Microbiology, bacteriology, virology, mycology, Mikrobiologi, bakteriologi, virologi, mykologi
Original languageEnglish
Awarding Institution
Supervisors/Assistant supervisor
  • [unknown], [unknown], Supervisor, External person
Award date2003 Mar 24
  • Department of Microbiology, Lund University
Print ISBNs91-628-4021-5
Publication statusPublished - 2000
Publication categoryResearch

Bibliographic note

Defence details Date: 2003-03-24 Time: 10:15 Place: Blue lecture hall, Ecology building, Sölvegatan 37, Lund External reviewer(s) Name: Guest, John R. Title: Prof Affiliation: FRS, Department of Molecular Biology and Biotechnology, University of Sheffield --- The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Biology building (Closed 2011) (011008000)