Haptoglobin–Haemoglobin Complexes studied by Polyacrylamide Gel Electrophoresis

Abstract

HAPTOGLOBIN, one of the α 2 globulins of human serum, is thought to combine irreversibly with haemoglobin in a molecular ratio of one to one^1,2. Two bands are therefore expected after gel electrophoresis of haptoglobin to which haemoglobin has been added in non-saturating proportions, a rapidly migrating band of free haptoglobin and a slower one for the haptoglobin–haemoglobin complex. Reported results are different. In agar gel electrophoresis, a single zone occurs with a mobility that decreases with increasing haemoglobin concentration. Two possible explanations are offered by Wieme³. Complex formation may be reversible, making it possible for a few haemoglobin molecules to interact with all of the haptoglobin molecules, resulting in a migration rate intermediate between free and fully saturated haptoglobin. More probably, the haptoglobin–haemoglobiri complex has residual binding capacity for other haptoglobin molecules. In this way the influence of one haemoglobin molecule extends over several molecules of haptoglobin. Both explanations are incompatible with the commonly held ideas about the character of the haptoglobin–haemoglobin complex. In starch gel, undersaturated haptoglobin type 1-1 (ref. 4) shows a complex with a mobility intermediate between that of the uncombined and the fully saturated protein. Laurell⁵ suggests that haptoglobin may pick up a half molecule of haemoglobin in these conditions.