Hirawake H, Taniwaki M, Tamura A, Kojima S, Kita K
Department of Parasitology, University of Tokyo, Japan.
Cytogenet Cell Genet. 1997;79(1-2):132-8. doi: 10.1159/000134700.
Complex II (succinate-ubiquinone oxidoreductase) is an important enzyme complex in both the tricarboxylic acid cycle and the aerobic respiratory chains of mitochondria in eukaryotic cells and prokaryotic organisms. In this study, the amino acid sequences of the large (cybL) and small (cybS) subunits of cytochrome b in human liver complex II were deduced from cDNAs isolated by homology probing with mixed primers for the polymerase chain reaction. The mature cybL and cybS contain 140 and 103 amino acids, respectively, and show little similarity to the amino acid sequences of the subunits from other species in contrast to the highly conserved features of the flavoprotein (Fp) subunit and iron-sulfur protein (Ip) subunit. From hydrophobicity analysis, both cybL and cybS appear to have three transmembrane segments, indicating their role as membrane-anchors for the enzyme complex. Histidine residues, which are possible heme axial ligands in cytochrome b of complex II, were found in the second transmembrane segment of each subunit. The genes for cybL (SDHC) and cybS (SDHD) were mapped to chromosome 1q21 and 11q23, respectively by fluorescent in situ hybridization (FISH).
复合物II（琥珀酸-泛醌氧化还原酶）是真核细胞和原核生物线粒体的三羧酸循环及有氧呼吸链中的一种重要酶复合物。在本研究中，通过用聚合酶链反应的混合引物进行同源性探测分离出的cDNA，推导了人肝脏复合物II中细胞色素b的大亚基（cybL）和小亚基（cybS）的氨基酸序列。成熟的cybL和cybS分别包含140和103个氨基酸，与黄素蛋白（Fp）亚基和铁硫蛋白（Ip）亚基的高度保守特征相比，它们与其他物种亚基的氨基酸序列几乎没有相似性。通过疏水性分析，cybL和cybS似乎都有三个跨膜区段，表明它们作为酶复合物膜锚定物的作用。在每个亚基的第二个跨膜区段中发现了组氨酸残基，它们可能是复合物II细胞色素b中的血红素轴向配体。通过荧光原位杂交（FISH）分别将cybL（SDHC）和cybS（SDHD）基因定位到染色体1q21和11q23。
