Structure, function and evolution of cyclostomata hemoglobin and myoglobin

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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.