PURIFICATION AND CHARACTERIZATION OF AN ARCHAEBACTERIAL SUCCINATE-DEHYDROGENASE COMPLEX FROM THE PLASMA-MEMBRANE OF THE THERMOACIDOPHILE SULFOLOBUS-ACIDOCALDARIUS

A succinate dehydrogenase complex was isolated in a three-step purification from plasma membranes of the thermoacidophilic archaebacterium Sulfolobus acidocaldarius. It consists of four subunits: a, 66 kDa; b, 31 kDa; c, 28 kDa and d, 12.8 kDa. In the 141-kDa native protein, the four subunits are present in an equimolar stoichiometry. The complex contains acid-non-extractable flavin, iron and acid-labile sulphide. Maximal succinate dehydrogenase activities were recorded at pH 6.5, which coincides with the internal pH of Sulfolobus cells. The temperature optimum of 81-degrees-C defines the Sulfolobus succinate dehydrogenase as a thermophilic enzyme complex. The K(m) for succinate was found to be 1.42 mM (55-degrees-C). Similar to the mitochondrial soluble succinate dehydrogenase, this enzyme is capable of transferring electrons to artifical electron acceptors, for instance phenazine methosulfate, N,N,N',N'-tetramethyl-p-phenylenediamine and ferricyanide. In contrast to the mitochondrial succinate dehydrogenase, the archaebacterial enzyme reduces 1,4-dichloroindophenol also in the absence of phenazine methosulfate. Caldariella quinone, the physiological electron mediator in the Sulfolobus respiratory chain, was only slowly reduced under adjusted conditions. The succinate-phenazine methosulfate-(1,4-dichloroindophenol) oxidoreductase of the isolated complex was strongly inhibited by tetrachlorobenzoquinone. In plasma membranes the complex reduces molecular oxygen in a cyanide-sensitive reaction. Polyclonal Sulfolobus anti-a antibodies crossreacted with 66 - 67-kDa polypeptides from membranes of Thermoplasma acidophilium, Sulfolobus solfataricus and beef heart submitochondrial particles.