The contributions of G.T. (Jerry) Babcock to our understanding of cytochrome oxidase.
The contributions of G.T. (Jerry) Babcock to our understanding of cytochrome oxidase.
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G.T.的贡献
DOI：
10.1016/j.bbabio.2003.05.001
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发表时间：
2004
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影响因子：
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通讯作者：
Palmer,Graham
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作者：
Palmer,Graham
Jerry Babcock研究方法的标志是物理方法的创新应用，特别是新兴光谱技术的使用。因此，细胞色素氧化酶成为他关注的两个生物化学研究领域之一也就不足为奇了，因为我们对这种酶的了解极大地受益于光谱方法。对细胞色素氧化酶的第一次观察发生在100多年前，起源于CA MacMunn在19世纪最后十年的实验。使用低色散棱镜分光镜，MacMunn观察到各种组织在500-650 nm波长范围内包含四个波段。由于这些条带对生理刺激的反应相似，他将它们归因于一种单一的化合物，他称之为组织血红素[1]。不幸的是，这些观察在当时影响不大，原因有二。首先，在这个光谱范围内没有一种具有四个波段的化合物的原型，其次，当时试图重复他的研究并不成功。直到20世纪20年代，大卫·凯林（David Keilin）最初并不知道麦克穆恩的出版物，才能够证实他在一篇题为“关于细胞色素，一种呼吸色素，动物，酵母和高等植物共有”的论文中发表的原始观察结果。在这篇论文中，Keilin描述了他的重要观察，即在刚刚悬浮在水中的酵母中无法观察到MacMunn的四带光谱，但当他进行观察时，光谱出现了完整的强度。使用各种化学处理，Keilin得出结论，四带光谱实际上代表了三种化合物，每种化合物都有两条谱带。第一个窄带称为α，在三种化合物中具有显著不同的波长，而第二个带称为β，具有相似的波长，无法分辨。例如，在蜜蜂的胸部肌肉中，三个α带位于605、567和550 nm处; Keilin分别将这些化合物称为细胞色素a、B和c。13年后，可见光谱再次有助于确定细胞色素a实际上是两种相似的化合物，可以通过对呼吸抑制剂（如氰化物，叠氮化物和一氧化碳）的反应来区分[3]。第一种化合物保留了细胞色素a的名称，不受这些抑制剂的影响，而第二种化合物命名为细胞色素a3，是这些抑制剂的反应部位。在此期间，主要的进展是开发了制备高质量的洗涤剂增溶酶的程序，以及对酶及其抑制剂复合物的光学性质进行了更定量的表征，后者是由于Beckman DW-2和卡里11记录粘度计的开发。然而，甚至某些基本属性都还没有建立。例如，细胞色素a与细胞色素a3的摩尔比尚未确定。此外，虽然毫无疑问，酶的功能是使用细胞色素c作为电子供体将氧转化为水，但很少注意到该反应的机理。
The hallmark of Jerry Babcock’s approach to research was the innovative application of physical methods, in particular the use of emerging spectroscopic techniques. It is thus not surprising that cytochrome oxidase became one of the two research areas of biochemistry that received his attention, for our knowledge of this enzyme has benefited enormously from spectroscopic methodologies. The first such observation on cytochrome oxidase occurred more than 100 years ago and originated in the experiments of CA MacMunn during the last decade of the 19th century. Using a low-dispersion prism spectroscope, MacMunn observed that a variety of tissues contained four bands in the wavelength range 500–650 nm. Because these bands responded similarly to physiological stimuli, he ascribed them to a single compound that he called histohematin [1]. Unfortunately, these observations had little impact at the time for two reasons. First, there was no prototype for a compound with four bands in this spectral range, and second, contemporary attempts to repeat his studies were unsuccessful1. It was not until the 1920s when David Keilin, initially unaware of MacMunn’s publications, was able to confirm the original observations which he published in a paper titled ‘‘On cytochrome, a respiratory pigment, common to animals, yeast, and higher plants’’[2]. In this paper, Keilin described his crucial observation that MacMunn’s four-banded spectrum could not be observed in yeast that had been freshly suspended in water, but as he was making his observations, the spectrum appeared with full intensity. Using a variety of chemical treatments, Keilin was drawn to the conclusion that the four-banded spectrum actually represented three compounds, each of which had two bands. The first, a narrow band called alpha, had significantly different wavelengths in the three compounds while the second band, called beta, had similar wavelengths and could not be resolved. For example, in the thoracic muscles of the bee, the three alpha bands were located at 605, 567, and 550 nm; Keilin called these compounds cytochromes a, b, and c, respectively. Thirteen years later, the visual spectroscope was again instrumental in establishing that cytochrome a was actually two similar compounds distinguishable by their response to respiratory inhibitors such as cyanide, azide, and carbon monoxide [3]. The first compound, which retained the name cytochrome a, was unaffected by such inhibitors, while the second, named cytochrome a3, was the site of reaction of these inhibitors2.We now fast-forward 20 years. In the interim, the principal advances were the development of procedures for the preparation of high-quality, detergent-solubilized enzyme and a more quantitative characterization of the optical properties of the enzyme and its inhibitor complexes, the latter being due to the development of the Beckman DW-2 and Cary 11 recording spectrophotometers. However, even certain basic properties had yet to be established. For example, the molar ratio of cytochrome a to cytochrome a3 had not been firmly established. Furthermore, while it was unquestioned that the function of the enzyme was to convert oxygen to water using cytochrome c as electron donor, little attention had been paid to the mechanism of this reaction.