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

测定了来自日本Amami岛的Barbatia Lima的血红蛋白的两个结构域2D和单结构域增量链的基因结构。三角链是这种不寻常的双结构域链的祖先链，在来自日本高知的近缘文蛤B.reeveana和B.lima中没有表达。除了在脊椎动物珠蛋白基因中发现的传统的两个内含子外，Delta链基因还有一个预编码内含子。二维链上有预编码内含子和桥接内含子，它们与两个常规内含子一起分隔这两个结构域。核苷酸序列的比较表明，2D链是由两个祖先Delta基因的互换事件产生的。确定了深海文蛤Calysupgena soyoae血红蛋白的基因结构。令人惊讶的是，它没有预编码内含子，但在A-螺旋区域含有一个额外的内含子。这有力地表明，内含子会移动。我认为预编码内含子在产生显著的血红蛋白和肌红蛋白多样性中起着重要作用。我们检测了Barbatia lima(Amami)三种类型的血红蛋白的自氧化速率，它们是增量链的同源二聚体、α和β链的四聚体以及2D和增量链的聚合物。聚合血红蛋白具有很强的抗自氧化能力，其氧化速度比二聚体慢5倍。然而，该二聚体的速率与人类血红蛋白的速率相当，这表明Barbatia血红蛋白是相当稳定的分子。

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.