title: Familial secondary erythrocytosis due to increased oxygen affinity is caused by destabilization of the T state of hemoglobin Brigham (α₂β₂(Pro100Leu)).
abstract: Hemoglobin Brigham (β Pro100 to Leu) was first reported in a patient with familial erythrocytosis. Erythrocytes of an affected individual from the same family contain both HbA and Hb Brigham and exhibit elevated O₂ affinity compared with normal cells (P₅₀ = 23 mm Hg vs. 31 mmHg at pH 7.4 at 37°C). O₂ affinities measured for hemolysates were sensitive to changes in pH or chloride concentrations, indicating little change in the Bohr and Chloride effects. Hb Brigham was separated from normal HbA by nondenaturing cation exchange liquid chromatography, and the amino acid substitution was verified by mass spectrometry. The properties of Hb Brigham isolated from the patient's blood were then compared with those of recombinant Hb Brigham expressed in Escherichia coli. Kinetic experiments suggest that the rate constants for ligand binding and release in the high (R) and low (T) affinity quaternary states of Hb Brigham are similar to those of native hemoglobin. However, the Brigham mutation decreases the T to R equilibrium constant (L) which accelerates the switch to the R state during ligand binding to deoxy-Hb, increasing the rate of association by approximately twofold, and decelerates the switch during ligand dissociation from HbO₂, decreasing the rate approximately twofold. These kinetic data help explain the high O₂ affinity characteristics of Hb Brigham and provide further evidence for the importance of the contribution of Pro100 to intersubunit contacts and stabilization of the T quaternary structure.
authors: Laboratory of Biochemistry and Vascular Biology, Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892, USA.
authors: Todd L
authors: TL
authors: Mollan
authors: Bindu
authors: B
authors: Abraham
authors: Michael Brad
authors: MB
authors: Strader
authors: Yiping
authors: Y
authors: Jia
authors: Jay N
authors: JN
authors: Lozier
authors: John S
authors: JS
authors: Olson
authors: Abdu I
authors: AI
authors: Alayash
mesh_terms: D000328:Adult; D056148:Chromatography, Reverse-Phase; D005260:Female; D006454:Hemoglobins / Q000737:chemistry / Q000302:isolation & purification; D006455:Hemoglobins, Abnormal / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D010100:Oxygen / Q000378:metabolism*; D011086:Polycythemia / Q000097:blood / Q000151:congenital / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D006454:Hemoglobins; D006455:Hemoglobins, Abnormal; D011994:Recombinant Proteins; D010100:Oxygen