Gorr T, Kleinschmidt T, Fricke H
Max-Planck-Institut für Biochemie, Martinsried bei München, Germany.
Nature. 1991 May 30;351(6325):394-7. doi: 10.1038/351394a0.
The origin of tetrapods has been debated for many years. In traditional systematics, the extinct lobe-finned bony fish (Rhipidistia) are regarded as the closest relatives of tetrapods. Among living fish, the coelacanth Latimeria chalumnae (Actinistia), which is the only recent representative of the Crossopterygii (Actinistia and Rhipidistia), the lungfish (Dipnoi) and ray-finned fish (Actinopterygii), have each been considered as sister-groups of the tetrapods. We have now determined the sequence of the alpha- and beta-globin chains of coelacanth haemoglobin and compared them with all known haemoglobins of bony and cartilaginous fish as well as those of tadpoles and adult amphibians. Haemoglobins of bony fish match more closely those of larval than adult amphibians. The beta chains of Latimeria match those of tadpoles more closely (54%) than do those of any other fish, whereas the alpha chains of Latimeria (45.4%), and especially of teleosts (49.2%), are closer to those of larval amphibians than are those of lungfish (39.8%). If only synapomorphous sequence matches (those at derived positions shared by one bony fish and tadpoles but not by any other bony fish) are considered, both Latimeria globin chains have distinctly more identities with phase of tadpoles than do those of any bony fish. Thus the primary structure of Latimeria haemoglobin indicates that the coelacanth is the closest living relative of tetrapods.
四足动物的起源多年来一直存在争议。在传统分类学中，已灭绝的肉鳍硬骨鱼（扇鳍鱼类）被视为四足动物的近亲。在现存鱼类中，腔棘鱼拉蒂迈鱼（腔棘鱼纲）是扇鳍鱼亚纲（腔棘鱼纲和扇鳍鱼类）最近的唯一代表，肺鱼（角齿鱼目）和辐鳍鱼（辐鳍鱼纲）都曾被认为是四足动物的姐妹群。我们现已确定了腔棘鱼血红蛋白的α链和β链序列，并将它们与硬骨鱼和软骨鱼以及蝌蚪和成年两栖动物的所有已知血红蛋白进行了比较。硬骨鱼的血红蛋白与幼体两栖动物的血红蛋白比与成年两栖动物的血红蛋白更匹配。拉蒂迈鱼的β链与蝌蚪的β链匹配度更高（54%），高于其他任何鱼类，而拉蒂迈鱼的α链（45.4%），尤其是硬骨鱼的α链（49.2%），比肺鱼的α链（39.8%）更接近幼体两栖动物的α链。如果只考虑共衍征序列匹配（即一种硬骨鱼和蝌蚪共有的衍生位置上的匹配，而其他硬骨鱼没有），拉蒂迈鱼的两条球蛋白链与蝌蚪阶段的相同性明显高于任何硬骨鱼。因此，拉蒂迈鱼血红蛋白的一级结构表明腔棘鱼是现存与四足动物亲缘关系最近的物种。
