Molecular Stability and Function of Hb C-Harlem

Abstract

The oxygen binding property and molecular stability of Hb C-Harlem (Hb CH) (β6 Glu+Val, β73 Asp+Asn) were studied in comparison with those of Hb A and Hb S. The oxygen affinity and Bohr effect of purified Hb CH with and without organic phosphates were similar to those of purified Hb A and Hb S. The oxygen affinities of red cell suspensions obtained from the patient with Hb S-CH were lower than those of Hb S and Hb A. The level of 2,3-DPG was elevated by more than 50% of the normal level. The stability of various liganded forms of Hb CH was determined by mechanical shaking and heat denaturation. The oxy-, carbonmonoxy-, and met-forms of Hb CH were 2–3 times less stable than corresponding forms of Hb S during mechanical shaking. The results of the shaking experiments on deoxy-Hb CH differed drastically from those obtained on deoxy-Hb S, with deoxy-Hb CH being 17 times less stable than deoxy-Hb S. The rate of precipitation of the various ligands of Hb CH was pH dependent, with the rate being faster in an alkaline pH compared to an acid pH. The results of the heat stability tests of various liganded forms of Hb CH differed from the results of the mechanical shaking tests. The oxy-, met-, and carbonmonoxy-forms of Hb CH were less heat stable than similar ligands of Hb A and Hb S, but the heat stability of the deoxy-forms of Hb CH was similar to that of deoxy-Hb A and deoxy-Hb S. From these results the difference between the heat and mechanical shaking methods with respect to the molecular conformation of hemoglobin has been discussed.