Genetic Variation of the Dimeric Haemoglobin of the Bivalve Mollusc Anadara trapezia

Abstract

The bivalve mollusc A. trapezia has two haemoglobins, a tetrameric major haemoglobin, and a dimeric minor haemoglobin, the latter having two identical chains that are different from the chains in the tetramer. Genetic variation in the dimer results in two different haemoglobins, HbIIa and HbIIb, and it is known that the relative proportions of these two polymorphic forms vary with latitude along the eastern coastline of Australia. The HbIIb variant is more common at higher latitudes where water temperature may act as selecting agent. Comparative peptide mapping and amino acid analysis of peptides have shown that in HbIIa an aspartyl residue replaces the seryl residue found in HbIIb at residue 64, position E2 in the E helix. The E and F helices have recently been shown to be highly conserved in arcid globins and to be involved in subunit contacts in the cooperative dimers.