Cytochrome c and the evolution of energy metabolism.
Cytochrome c and the evolution of energy metabolism.
复制标题
细胞色素 c 和能量代谢的进化。
DOI：
10.1038/scientificamerican0380-136
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发表时间：
1980
影响因子：
3
通讯作者：
R. E. Dickerson
中科院分区：
文献类型：
--
作者：
R. E. Dickerson
每个人都曾有过时间旅行的幻想，也许包括能够回到过去，看看地球上的早期生命是什么样子，以及这一切是如何开始的。寻求开端的冲动几乎是人类的一种冲动，它在宗教、历史和最近的科学中找到了出路。查尔斯·达尔文的进化论最吸引人的地方之一是，它提供了一个理性的框架，让我们思考与地球上生命历史有关的现有证据。有两种经典的进化证据：一种是关于今天的生物体的信息，另一种是可以从化石记录中读到的关于早期生命的更零碎的信息。在这篇文章中，我将报告最近的努力，扩大图片的基础上的分子证据：三维折叠和氨基酸序列的蛋白质分子。化石故事本身可以合理地追溯到6亿年前的寒武纪时期，这一时期以后生动物（多细胞生物）的爆炸性辐射为标志，留下了容易辨认的化石遗迹。前寒武纪的化石证据更难获得，但它仍然是信息丰富的。一些软体后生动物的化石可以追溯到8亿或10亿年前，单细胞生物可能是真核生物（DNA组织在细胞核内的细胞），如理查德·E.迪克森是14亿年。细菌的踪迹可以追溯到34亿年前。化石脊椎动物留下了许多可以比较的特征，从中可以推断出进化史：不仅是骨骼结构，还有牙齿、皮肤或毛发的印记、消化的粪便、甚至脚印。相比之下，化石细菌在岩石的显微切片上只留下一条模糊的细胞边界线。这使得进化生物学家的任务更加困难。如果真核生物的生命形式是由它们的解剖结构来区分的，那么细菌是由它们的代谢来区分的，而代谢途径几乎不留下锡尔斯。人们可以从硫酸盐、铁或碳酸盐的沉积物中推断出，这些化合物是生命形式曾经存在的最终产物，但这并不能告诉人们很多关于生命形式本身或它们之间的关系。然而，情况并不像前面所说的那样暗淡。在过去的15年里，一整套新的进化证据来自分子水平的研究：对蛋白质三维结构和氨基酸序列的分析（以及最近对DNA中核苷酸序列的分析）。具有相同代谢的生物体具有相同的酶，尽管在不同的生物体中，这些酶以相同的方式起作用，并且具有非常相似的三维结构，但它们在来自呼吸细菌铜绿假单胞菌的氨基细胞色素C551分子的序列细节上可能不同。图中，蛋白质主链的α碳原子（编号）和从其上分支出的分支侧链都是彩色的，以强调血红素基团在分子的疏水性（防水性）内部的主要作用方式，只有一个边缘
Everybody at one time or another has had fantasies about time trav el, perhaps including being able to go back in time to see what early life on the earth was like and how it all started. The urge to seek out beginnings is al most a compulsion in the human spe cies, and it has found outlets in religion, in history and more recently in science. One of the great attractions of Charles Darwin's theory of evolution was that it provided a rational framework for thinking about the available evidence bearing on the history of life on the earth. There are two kinds of classical evolutionary evidence: information con cerning living organisms as they are to day and more fragmentary information about earlier life that can be read in the fossil record. In this article I shall report recent efforts to enlarge the picture on the basis of molecular evidence: the three-dimensional folding and the ami no acid sequences of protein molecules. The fossil story itself can be extended back with reasonable confidence to the beginning 600 million years ago of the Cambrian period, an interval marked by the explosive radiation of the metazoans (multicelled organisms), which left easi ly discernible fossil remains. The Pre cambrian fossil evidence is harder to get, but it is still informative. There are fossils of a few soft-bodied metazoans that go back to 800 or 1,000 million years ago and of one-celled organisms that may be eukaryotes (cells whose DNA is organized within nuclei) as old by Richard E. Dickerson as 1.4 billion years. Traces of prokary otes (bacteria) go back 3.4 billion years. Fossil vertebrates leave many traits that can be compared and from which evolutionary history can be deduced: not only bone structures but also teeth, imprints of skin or hair, fossilized stom ach contents and feces and even foot prints. Fossil bacteria, in contrast, often leave nothing more than a shadowy out line of a cell boundary in microscopical ly thin sections of rock. This makes the task of the evolutionary biologist much harder. If eukaryotic life forms are dis tinguished by their anatomy, bacteria are distinguished by their metabolism, and metabolic pathways leave few fos sils. One can infer from deposits of sul fates, iron or carbonates that life forms once existed for which these compounds were end products, but this does not tell one very much about either the life forms themselves or their relationships. And yet the situation is less bleak than the foregoing might suggest. Over the past 15 years an entire new body of evo lutionary evidence has come from stud ies at the molecular level: analyses of the three-dimensional structure of pro teins and the sequence of amino acids in them (and more recently of the sequence of nucleotides in DNA). Organisms hav ing the same metabolism have the same enzymes, and although in different or ganisms those enzymes function in the same way and have quite similar three dimensional structures, they can differ in details of the seq uence of the aminoCYTOCHROME C551 MOLECULE from the respiring bacterium Pseudomonas aeruginosa has a rosette-shaped, iron-containing heme group wrapped in a protein chain consisting of 82 amino acids. Here the alpha carbon atoms (numbered) of the main chain of the protein and the side chains that branch from them are colored (see key) to emphasize the way the heme group is largely huried in the molecule's hydrophohic (water-repellent) interior, with only one edge