Abstract
An active respiratory complex II (succinate:quinone oxidoreductase) has been purified from tetraether lipid membranes of the thermoacidophilic archaeon, Sulfolobus sp. strain 7. It consists of four different subunits with apparent molecular masses of 66, 37, 33, and 12 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The 66-kDa subunit contains a covalently bound flavin, the 37-kDa subunit is a possible iron-sulfur protein carrying three distinct types of EPR-visible FeS cluster, and the 33- and 12-kDa subunits are putative membrane-anchor subunits, respectively. While no heme group is detected in the purified complex II, it catalyzes succinate-dependent reduction of ubiquinone-1 and 2,6-dichlorophenolindophenol in the absence of phenazine methosulfate. The respiratory complex II of Sulfolobus sp. strain 7 appears to be novel in that it functions as a true succinate:caldariellaquinone oxidoreductase, although inherently lacking any heme group. This further indicates that the heme group of several respiratory complexes II may not be involved in the redox intermediates of the electron transfer from succinate to quinone.
Highlights
The respiratory complex II is an iron-sulfur flavoprotein complex which serves as the sole membrane-bound component of the tricarboxylic acid cycle and one of the most important entry sites into the aerobic respiratory chain of a variety of aerobic organisms [1,2,3]
In the preceding papers [29, 30], we reported the detailed properties of the membrane-bound cytochromes of Sulfolobus sp. strain 7, and the purification, characterization, in vitro reconstitution, and the resolution analysis of the archaeal terminal oxidase supercomplex containing four distinct heme centers (b562, a583, and aa3), one copper, and a Rieske-type FeS cluster
We report the purification and characterization of the respiratory complex II from Sulfolobus sp. strain 7
Summary
The respiratory complex II (succinate:quinone oxidoreductase) is an iron-sulfur flavoprotein complex which serves as the sole membrane-bound component of the tricarboxylic acid cycle and one of the most important entry sites into the aerobic respiratory chain of a variety of aerobic organisms [1,2,3]. FAD binds covalently to the largest flavoprotein subunit (ϳ60 –75 kDa) via 8␣-N3-histidyl linkage, and all FeS clusters are probably located in the second largest iron-sulfur subunit (ϳ25–30 kDa) These two subunits constitute a peripheral portion of complex II, which can function as a water-. For succinate:quinone oxidoreductase activity, two (or one in Bacillus subtilis enzyme [5]) smaller membranespanning subunits are required [2] These hydrophobic subunits contain low-potential b-type cytochrome(s). The primary structural comparison suggest that the membrane-anchor subunits are less homologous [3, 12] compared to the cases of the flavoprotein and iron-sulfur subunits of mitochondrial and aerobic bacterial respiratory complexes II [2, 3, 13,14,15,16]. This complex II appears to be novel in that it inherently lacks any heme group, while it can function as a succinate:caldariellaquinone oxidoreductase in vitro
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