Evolution of the unusual two-domain hemoglobin from the blood clam Barbatia lima, and its physiological properties.

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The gene structure of two-domain 2D and single domain delta chains of hemoglobins from the blood clam Barbatia lima, corrected from Amami Island, Japan, has been determined. The delta chain is the ancestral chain for the unusual two-domain chain, and has not been expressed in the closely related clams B.reeveana and B.lima from Kochi, Japan. The delta chain gene had a precoding-intron, in addition to the conventional two introns, which are found in vertebrate globin genes. The 2D chain had the precoding-intron and bridge-intron, that separates the two domains, together with the two conventional introns. Comparison of the nucleotide sequences suggested that the 2D chain was generated by crossing-over event of the two ancestral delta genes.The gene structure of hemoglobins from the deep-sea clam Calyptogena soyoae has been determined. Surprisingly, it contained no precoding-intron but contained an additional intron in A-helix region. This strongly suggests that intron moves. I suppose that the precoding-intron play an important role in generating the remarkable diversity of hemoglobins and myoglobins.The autoxidation rate of three types of hemoglobins, a homodimeric dimer of delta chain, a tetramer of alpha and beta chain and a polymer of 2D and delta chains, of Barbatia lima (Amami) has been examined. The polymeric hemoglobin was highly resistant to autoxidation, and the rate was 5 times slower that of the dimer. However the rate of the dimer was comparable to that of human hemoglobin, indicating barbatia hemoglobins are rather stable molecules.