環形動物アオゴカイPerinereis aibuhitensis巨大ヘモグロビンのグロビン鎖に含まれる希有なSS結合

The extracellular hemoglobin (Hb) from the polychaete Perinereis aibuhitensis consists
of four types of 144 globins and two types of 36 linker chains，having a molecular mass of about 3,500
kDa. There are two types of globin subunits: monomer chain a and disulfide-bondedt rimer AbB. The
amino acid sequences of the four globin chains (a，A ，b ，B ) were already reported，previously
(Yamanaka，M. et al. Natural Science Research of Tokushima University, 19, 63-92, 2005). The site of
disulfide bonds in the globin subunits have been investigated. Each globin chain contains an intrachain
disulfide bond between N-terminal and C-terminal Cys residues. In addition，the interchain disulfide
bonds were found between chains A and b，and b and B. Therefore，it is elucidated that the chain b is
situated at the center of disulfide-bonded trimer，such as A-b-B.The sites of disulfide-bonds determined
all could be suitably fitted to the tree dimensional structure of each subunit in a model without
stretching or twisting. It was also confirmed that there is no free Cys residue in Peinereis globins. The
positions of Cys residues of Perinereis globin sequences were compared wIth those of other 27 chains
derived from the homologous Hbs. Among 31 sequences，Cys residues were distributed in six sites.
The sites 1 and 2 are located at the N-terminal region of amino acid sequences，the sItes 3 and 4 at the
central region，and the sites 5 and 6 at C-terminal region. Furthermore，the Cys distribution was
categorized into eight patterns. Perinereis Hb has four patterns I，IV，VII，VIII，be ing lack of the central
sites 3 and 4. It should be noted that the pattern II includes the unique globins from Hbs of Lamellibrachia，Riftia
and Oligobrachia that carry H2S to the symbiotic bacteria，suggesting that these globin chains might carry H2S in
vivo. The phylogenetic tree of 31 globin chains derived from the giant Hbs is divided into two families A and B，
as already poited out by us Previously. The family A indudes pattern I-V，whereas the family B includes V-
VIII.