The Isoelectric Point of Adsorbed Hemo- Globin*

It is well established that various proteins, as gelatin and albumin, can be adsorbed on various adsorbents so that the proteincoated particle of adsorbent behaves electrophoretically as a particle of protein (Loeb, 1923; Freundlich and Abramson, 1928). Dummett and Bowden (1933) have recently reported, however, that the behavior of adsorbed hemoglobin varies with the adsorbent surface. Thus, when ox hemoglobin was added in sufficient concentration to coat completely particles of quartz, evacuated blood charcoal, and colloidal copper, respectively, the isoelectric point on quartz was 5.82, on charcoal 5.83, and on copper 6.72. They postulate a binding of some of the ionized groups of hemoglobin by the adsorbent surface. While this interpretation of their results is reasonable, it is not the only one possible. The other possibility is that. other substances of lower isoelectric points than hemoglobin might have been present and preferentially adsorbed. Since no one can guarantee that any sample of hemoglobin is 100 per cent pure, a decision between the two possibilities may be reached by observing whether or not the isoelectric point of adsorbed hemoglobin approaches that obtained by the moving boundary method as the purity of the sample of adsorbed hemoglobin is increased. This we have done and find that the isoelectric point of adsorbed hemoglobin does approach that of freely dissolved hemoglobin with increasing purity. This indicates that Dummett and Bowden’s results were due to impurities of lower isoelectric point than hemoglobin. Since the impurities may be preferentially adsorbed, a