Mangum C P
Am J Physiol. 1985 May;248(5 Pt 2):R505-14. doi: 10.1152/ajpregu.1985.248.5.R505.
The distribution of the O2 carrying proteins suggests that the original transport system was a hemoglobin similar to the alpha-chain of hemoglobin A and packaged in a nucleated red blood cell. These molecules, which occur in large open fluid compartments, function as O2 stores for regular periods of hypoxia as well as carriers between sites of gas exchange. When the closed circulatory system first arose, the red blood cell was abandoned in favor of extracellular heme proteins, and the O2 storage function became less important. Alternative O2 carriers, hemerythrins, appear in the blood at about the same phylogenetic level as the intracellular hemoglobins, and their respiratory functions appear to be similar. The presence of hemoglobins instead of hemerythrins in the vertebrates may be an evolutionary accident. Still other O2 carriers, hemocyanins, arose separately in two specialized groups that left no descendants. Their O2 binding has all the adaptive features of vertebrate hemoglobin O2 binding, with unique features also. The respiratory function of the hemocyanins is largely limited to O2 transport, which makes a far greater contribution to aerobic metabolism than the O2 carriers found in simpler systems.
携带氧气的蛋白质的分布表明，最初的运输系统是一种类似于血红蛋白A的α链的血红蛋白，并包装在有核红细胞中。这些分子存在于大型开放的流体隔室中，在定期缺氧期间充当氧气储存库，同时也是气体交换部位之间的载体。当封闭的循环系统首次出现时，红细胞被舍弃，转而青睐细胞外血红素蛋白，氧气储存功能变得不那么重要。另一种氧气载体血红细胞素，在系统发育水平上与细胞内血红蛋白大致相同的时候出现在血液中，并且它们的呼吸功能似乎相似。脊椎动物中存在血红蛋白而非血红细胞素可能是一个进化上的偶然事件。还有其他的氧气载体血蓝蛋白，分别在两个没有后代的特殊类群中出现。它们与氧气的结合具有脊椎动物血红蛋白与氧气结合的所有适应性特征，也有独特的特征。血蓝蛋白的呼吸功能主要限于氧气运输，这对有氧代谢的贡献比在更简单系统中发现的氧气载体大得多。
