The hemoglobin system of the hagfish Myxine glutinosa: aggregation state and functional properties

Abstract

Hemoglobin (Hb) from the hagfish Myxine glutinosa is composed of six major monomeric subunits. Some of these subunits aggregate to dimers at low pH, and to tetramers when deoxygenated and at high protein concentration. The aggregation is inhibited by the presence of KCl. Oxygen equilibrium studies show the presence of a small Bohr effect which is strongly reduced by KCl, indicating that it originates from pH-dependent aggregation. ATP and DPG cause a similar decrease in the Bohr effect. O 2 affinity is dependent on protein concentration, temperature and presence of CO 2. Cooperativity is practically absent. O 2 binding properties of the separated aggregating and non-aggregating Hbs purified at low pH cannot account for the functional properties of the composite hemolysate, suggesting the presence of other subunits interactions. The results are discussed in relation to literature data for other cyclostome Hbs and for M. glutinosa Hb, where the presence of three major monomeric Hbs and a possible CO 2-dependent aggregation had been reported.