Refojo Patrícia N, Teixeira Miguel, Pereira Manuela M
Instituto de Tecnologia Química e Biológica, Universidade Nova de Lisboa, Av. da República, EAN, 2780-157 Oeiras, Portugal.
Biochim Biophys Acta. 2010 Aug;1797(8):1477-82. doi: 10.1016/j.bbabio.2010.02.029. Epub 2010 Mar 4.
An alternative complex III (ACIII) is a respiratory complex with quinol:electron acceptor oxidoreductase activity. It is the only example of an enzyme performing complex III function that does not belong to bc1 complex family. ACIII from Rhodothermus (R.) marinus was the first enzyme of this type to be isolated and characterized, and in this work we deepen its characterization. We addressed its interaction with quinol substrate and with the caa3 oxygen reductase, whose coding gene cluster follows that of the ACIII. There is at least, one quinone binding site present in R. marinus ACIII as observed by fluorescence quenching titration of HQNO, a quinone analogue inhibitor. Furthermore, electrophoretic and spectroscopic evidences, taken together with mass spectrometry revealed a structural association between ACIII and caa3 oxygen reductase. The association was also shown to be functional, since quinol:oxygen oxidoreductase activity was observed when the two isolated complexes were put together. This work is thus a step forward in the recognition of the structural and functional diversities of prokaryotic respiratory chains.
交替型细胞色素c氧化酶复合体III（ACIII）是一种具有喹醇：电子受体氧化还原酶活性的呼吸复合体。它是执行细胞色素c氧化酶复合体III功能但不属于bc1复合体家族的酶的唯一实例。来自海栖热袍菌（Rhodothermus marinus，简称R. marinus）的ACIII是此类中首个被分离和表征的酶，在本研究中我们对其表征进行了深入探究。我们研究了它与喹醇底物以及caa3氧还原酶的相互作用，caa3氧还原酶的编码基因簇紧跟在ACIII的编码基因簇之后。通过对醌类似物抑制剂HQNO进行荧光猝灭滴定观察到，R. marinus ACIII中至少存在一个醌结合位点。此外，电泳和光谱证据，以及质谱分析共同揭示了ACIII与caa3氧还原酶之间的结构关联。这种关联也被证明具有功能性，因为当将两个分离的复合体放在一起时可观察到喹醇：氧氧化还原酶活性。因此，这项研究在认识原核生物呼吸链的结构和功能多样性方面向前迈进了一步。
