Structures of the deoxy and CO forms of haemoglobin from Dasyatis akajei, a cartilaginous fish

The three-dimensional structures of the deoxy- and carbon-monoxyhaemoglobin (Hb) from Dasyatis akajei, a stingray, have been determined at 1.6 and 1.9 Angstrom resolution, respectively. This is one of the most distantly relat ed vertebrate Hbs to human HbA. Both structures resemble the respective for ms of HbA, indicating that the alpha(2)beta(2)-type tetramer and the mode o f the quaternary structure change are common to Hbs of jawed vertebrates. L arger deviations between D. akajei Kb and human HbA are observed in various parts of the molecule, even in the E and F helices. Significant mutations and/or conformational changes are also observed around the haems, in the C- terminal region of the beta subunit, in the alpha(1)beta(2) interface and i n the organic phosphate-binding site of HbA. Despite these structural diffe rences, the oxygen affinity, haem-haem interaction, Bohr effect and organic phosphate effect of D. akajei Hb are all only moderately reduced. Compared with human HbA, the overall r.m.s. deviation of main-chain atoms in the he lical regions of bony fish Hbs is smaller than that of D. akajei Hb.