Structure, function and evolution of cyclostomata hemoglobin and myoglobin

为了阐明在进化上连接单体和四聚体血红蛋白的圆口动物肌红蛋白和血红蛋白的结构和功能，我们从新泻和北海道的七鳃鳗的血液和肌红蛋白制备了溶血产物和血红蛋白样品，1.血红蛋白和肌红蛋白的组成和结构分析（Hb I-Hb V），前两者为主要成分。(2)血红蛋白I的氨基酸序列与七鳃鳗血红蛋白V的同源性为97%。与人血红蛋白α链和β链同源性较低，氨基端长8个残基，羧基端缺失9个残基。(3)Hb II的氨基酸序列与Hb I相同。(4)2.氧结合特性（1）七鳃鳗血红蛋白与脊椎动物血红蛋白相比，其氧结合功能较为原始，即协同性弱，玻尔效应和CO_2效应减弱，缺乏有机磷酸盐的作用。(2)Hb与Hb Ⅱ在功能上存在一定差异。(3)3.电子顺磁共振（EPR）和傅立叶变换红外吸收（FT-IR）（1）氧化态（met）和还原态（CO）的EPR和FT-IR表明七鳃鳗血红蛋白的血红素-铁配位结构与脊椎动物血红蛋白的结构相似，其近端和远端残基均为His。Hb II可以通过一些人工或翻译后过程从Hb I衍生而来。(2)在七鳃鳗中，肌红蛋白可以与血红蛋白相同。如果是这样的话，在这种动物或圆口动物中，血红蛋白被转化为肌红蛋白，从进化的角度来看是有趣的。

To clarify the structure and function of cyclostomata myoglobin and hemoglobin that evolutionally links the monomeric and tetrameric hemoglobins, we prepared hemolysate and hemoglobin samples from the blood and myoglobin from the skeletal muscle of river lampreys in Niigata and Hokkaido, and carried out the following studies.1.Components and structural analysis of hemoglobin and myoglobin(1) There were five isoforms (Hb I -Hb V) in the hemolysate and the first two were the major components. (2) The amino acid sequence of Hb I showed a 97% homology with Hb V for see lamprey. It showed less homology with the human Hb α chain and β chain, the amino terminal being longer by 8 residues and the carboxyl terminal having 9-residue deletions. (3) The amino acid sequence for Hb II was identical with that for Hb I. (4) Myoglobin was of single component and its amino acid sequence was identical with that for Hb I.2.Oxygen binding characteristics(1) In comparison with the vertebrate hemoglobin, the function of lamprey Hb is primitive in various aspects, namely, week cooperativity, a reduced Bohr effect and CO_2 effect and lack of the effect of organic phosphates. (2) There were some differences in function between Hb land Hb II. (3) The function of myoglobin was similar to that of Hb I.3.Electron paramagnetic resonance (EPR) and Fourier-transform infrared absorption (FT-IR)(1) EPR for oxidized (met) and reduced NO derivatives and FT-IR for CO derivative indicated that the heme-iron coodination structure for lamprey Hb resembles that for the vertebrate Hb in which the proximal and distal residues are His.4.Summary(1) Hb II can have been derived from Hb I through some artificial or post-translational process. (2) In lamprey, myoglobin can be identical with hemoglobin. If so, in this animal or in cyclostomata, hemoglobin as it is deverted to myoglobin, being interesting from the view point of evolution.