Amino-acid sequences of the alpha- and beta-subunits of hemerythrin from Lingula reevii

The complete amino-acid sequences of the α- and β-subunits of hemerythrin form the brachiopod Lingula reevii have been determined. These subunits are round in equal proportions in coelomic hemerythrocytes and form an octamer, presumably with an α4β4 composition. Both subunits were found to consist of 117 residues and to show 65% sequence identity to each other. Sequences of the α-and β-subunits of L. reevii hemerythrin are closely related to their counterparts in hemerythrin from the related brachiopod, Lingula unguis, showing 95% and 87% sequence identities, respectively. Sequence alignments show that 25 residues in the lingulid hemerythrin subunits are identical to those found in other hemerythrins and myohemerythrins. These conserved residues include those known to provide iron ligands. However, these comparisons also indicate that the lingulid hemerythrin sequences are distinct from those of the sipunculid and annelid hemerythrins and myohemerythrins.