Santucci R, Fiorucci L, Sinibaldi F, Polizio F, Desideri A, Ascoli F
Dipartimento di Medicina Sperimentale e Scienze Biochimiche, Università di Roma "Tor Vergata,", Rome, Italy.
Arch Biochem Biophys. 2000 Jul 15;379(2):331-6. doi: 10.1006/abbi.2000.1885.
The structural and redox properties of a heme-containing fragment (1-56 residues) of cytochrome c have been investigated by spectroscopic (circular dichroism, electronic absorption, and EPR) and voltammetric techniques. The results indicate that the N-fragment lacks ordered secondary structure and has two histidines axially bound to the heme-iron (the native His18 and a misligated His26 or His33). Despite the absence of ordered secondary structure, the peptide chain shields the heme group from solvent, as shown by (i) the pK(a) of protonation of the nonnative histidine ligand (5.18 +/- 0.05), lower than that of the bis-histidine guanidine-unfolded cytochrome c (5.58 +/- 0.05), and (ii) the redox potential, E(o) = 0 +/- 5 mV versus NHE, close to that of bis-histidine cytochrome c mutants but less negative than that of bis-histidine complexes of microperoxidase with short peptides. The electroactive N-fragment may be taken as a "minichrome c" model, with interesting potential for application to biosensor technology; further, the system provides useful information for a deeper understanding of cytochrome c folding and structural/functional organization.
通过光谱技术（圆二色性、电子吸收和电子顺磁共振）和伏安法对细胞色素c含血红素片段（1 - 56个残基）的结构和氧化还原性质进行了研究。结果表明，N端片段缺乏有序的二级结构，有两个组氨酸轴向结合到血红素铁上（天然的His18以及错配的His26或His33）。尽管缺乏有序的二级结构，但肽链可保护血红素基团免受溶剂影响，这表现为：（i）非天然组氨酸配体质子化的pK(a)（5.18±0.05）低于双组氨酸胍基展开的细胞色素c的pK(a)（5.58±0.05）；（ii）相对于标准氢电极，氧化还原电位E(o)=0±5 mV，接近双组氨酸细胞色素c突变体的电位，但比微过氧化物酶与短肽的双组氨酸复合物的电位负性小。该电活性N端片段可被视为一种“微型细胞色素c”模型，在生物传感器技术应用方面具有有趣的潜力；此外，该系统为更深入理解细胞色素c的折叠以及结构/功能组织提供了有用信息。
