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首页> 外文期刊>Biochimica et Biophysica Acta. Protein Structure and Molecular Enzymology >Structural basis for the electron transfer across the chromaffin vesicle membranes catalyzed by cytochrome b_(561): analyses of cDNA nucleotide sequences and visible absorption spectra
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Structural basis for the electron transfer across the chromaffin vesicle membranes catalyzed by cytochrome b_(561): analyses of cDNA nucleotide sequences and visible absorption spectra

机译：细胞色素b_（561）催化电子跨过嗜铬囊泡膜转移的结构基础：cDNA核苷酸序列和可见吸收光谱的分析

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摘要

We isolated cDNA clones for cytochromes b_(561) from sheep and porcine adrenal medullae using the RT-PCR technique. Comparison of the deduced amino acid sequences of various species showed that there are two fully-conserved regions in this cytochrome. In addition, one methionyl and six histidyl residues (potential heme ligands) are fully-conserved. Based on a plausible structural model in which a polypeptide spans the vesicle membranes six times and holds two heme B molecules, the first conserved sequence (~(69)ALLVYRVFR~(77)) is located on the extravesicular side of an α-helical segment and the second one (~(120)SLHSW~(124)) is located in an intravesicular loop connecting two α-helical segments, respectively. Consideration of the relative locations of the fully-conserved sequences, and the methionyl and histidyl residues in the model led to a proposal that the first and second conserved sequences are likely to form the binding sites for extravesicular ascorbic acid and intravesicular semidehydroascorbic acid, respectively. A mild alkaline-treatment of purified bovine cytochrome b_(561) in oxidized state led to a specific loss of an electron-accepting ability from ascorbic acid for a half of the heme center, suggesting a distinct role for each of the two hemes.
机译：我们使用RT-PCR技术从绵羊和猪肾上腺髓质中分离了细胞色素b_（561）的cDNA克隆。各种物种推导的氨基酸序列的比较表明，该细胞色素中有两个完全保守的区域。此外，一个甲硫酰基和六个组氨酸残基（潜在的血红素配体）是完全保守的。基于一个合理的结构模型，其中多肽跨六次囊泡膜并容纳两个血红素B分子，第一个保守序列（〜（69）ALLVYRVFR〜（77））位于α螺旋片段的囊泡侧第二个（〜（120）SLHSW〜（124））分别位于连接两个α螺旋段的囊内环中。考虑到完全保守序列的相对位置，以及模型中的甲硫酰基和组氨酸残基，导致提出这样一个建议，即第一和第二保守序列可能分别形成囊外抗坏血酸和囊内半脱氢抗坏血酸的结合位点。在氧化状态下，对纯化的牛细胞色素b_（561）进行温和的碱处理会导致抗坏血酸半个血红素中心的电子接受能力发生特定损失，表明这两个血红素各自具有独特的作用。

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