The alternative complex III from Rhodothermus marinus - a prototype of a new family of quinol: electron acceptor oxidoreductase

Dissertation presented to obtain a PhD degree in Biochemistry at the Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa

The aim of the work presented in this thesis was the characterization of a complex with quinol: electron carrier oxidodoreductase activity present in the membranes of the thermohalophilic bacterium Rhodothermus (R.) marinus. The complexes involved in the R. marinus respiratory chain have been extensively studied in the past few years. Specifically, the purification and characterization of a complex I (NADH: quinone oxidoreductase), a complex II (succinate:quinone oxidoreductase) and of three different oxygen reductases from the heme-copper oxygen reductases superfamily have been performed. Since those oxygen reductases are unable to receive electrons from quinol molecules, the presence of a complex linking complexes I and II to the oxygen reductases was needed. In fact, a complex with quinol: HiPIP oxidoreductase activity was purified and partially characterized. The absence of the Rieske protein indicated that the complex isolated from R. marinus has a different composition when compared with the typical cytochrome bc1 complex.(...)