| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1993: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1992: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1991: ¥1,200,000 (Direct Cost: ¥1,200,000)
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| Research Abstract |
Globins from the chiton, Liolophura japonica and blood clam, Barbatia virescens were investigated.
1. The blood clam B.virescens has a heterodimeric hemoglobin in erythrocytes. The complete amino acid sequence of chain I of B.virescens has been determined. The sequence was mainly determined from CNBr-peptides and their subpeptides, an the alignment of the peptides was confirmed by sequencing of PCR-amplified cDNA for B.virescens chain I.The cDNA-derived amino acid sequence matched completely with the sequence proposed from protein sequencing. An evolutionary tree for Anadara and Barbatia chains clearly indicates that all of the chains are evolved from one ancestral glolin gene, and that the divergence of chains has occurred in each clam after the speciation. The evolutionary rate for clam hemoglobins was estimated to be about four times faster than that of vertebrate hemoglobin. We suggest that blood clam hemoglobin is a physiologically less important molecule when compared with vertebr
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ate hemoglobins, and so it evolved rapidly and resulted in a remarkable diversity in quaternary and subunit structure within a relatively short period.
2. Myoglobin was isolated from the radular muscle of the chiton, L.japonica, a primitive archigastropodic mollusc. Liolophura contains three monomeric myoglobins(I,II,III), and the complete amino acid sequence of myoglobin I has been determined. The E7 distal histidine is conserved in Liolophura myoglobin. The autoxidation rate at physiological conditions indicated that Liolophura oxymyoglobin is fairly stable when compared with other molluscan myoglobins, A phylogenetic tree was constructed from 19 molluscan globin sequences. Liolophura myoglobin was placed on the branch of monomeric myoglobin lineage, showing that it diverged earlier from other monomeric myoglobins. The hemoglobin cluster is also divided into two subclusters. One cluster contains homodimeric, heterodimeric, tetrameric, and didomain chains of erythrocyte hemoglobins of the blood clam. Other cluster consists of three hemoglobin chains derived from the bacterial symbiont-harboring clams Calyptogena and Lucina, in which hemoglobins are suppossed to play an important role in maintaining the symbiosis withsulfide bacteria. Less
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