Structural and functional studies on hemoglobin Bethesda (α₂β₂^{145 His}), a variant associated with compensatory erythrocytosis

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Abstract

Studies have been performed on a 12-yr-old Chinese girl with compensatory erythrocytosis due to the presence of hemoglobin Bethesda comprising about 45% of the red cell hemoglobin. Her parents and three siblings were normal. The oxygen affinity of her blood was markedly increased: under physiological conditions (pH 7.40, 37°C). P50 was 12.8 mm Hg (normal = 26.5 mm Hg). The red cell 2,3-diphosphoglycerate (2.3-DPG) level was normal. The abnormal hemoglobin could not be separated from hemoglobin A by zone electrophoresis at pH 8.6 or isoelectric focusing on polyacrylamide gel. However, after the hemoglobin was split into free α and β chains by treatment with p-hydroxymercuribenzoate (PMB) or 6 M urea, an abnormal β chain was readily demonstrated having a higher isoelectric point (more positive net charge) than normal βA. Structural analysis of the variant β chain demonstrated the substitution of histidine for tyrosine at position 145: hemoglobin Bethesda (α2β2145His). From earlier chemical and crystallographic studies, it has been postulated that this residue is a critical determinant of hemoglobin function. Hemoglobin Bethesda was separated from hemoglobin A by column chromatography. Oxygen equilibria of purified hemoglobin Bethesda revealed an extremely high oxygen affinity (exceeding that of isolated α and β chains), and markedly reduced cooperativity. The Bohr effect of hemoglobin Bethesda was 1/3 that of hemoglobin A. However, hemoglobin Bethesda showed a significant interaction with 2.3-DPG and inositol hexaphosphate.

Authors

H. Franklin Bunn, Thomas B. Bradley, William E. Davis, James W. Drysdale, John F. Burke, William S. Beck, Myron B. Laver