Haemoglobin Rahere (beta Lys-Thr): A new high affinity haemoglobin associated with decreased 2, 3-diphosphoglycerate binding and relative polycythaemia.

Abstract

The laboratory tests carried out by standard methods' gave the following results: haemoglobin 19-0 g/dl; packed cell volume 57%; red blood count 6 x 1012/1 (6 000 000/mm3); mean cell volume 95 fl (95 1iM3); mean cell haemoglobin 32 pg; mean cell haemoglobin concentration 33 g/dl; reticulocytes 044%; white blood count 13-5 x 109/1 (13 500/mm3), with a neutrophil leucocytosis; platelets 275 x 109/1 (275 OOO/mm3). All these results were the mean values of 18 determinations over one and a half years. Blood volume studies performed on two occasions using 51Cr-labelled red cells and "3'Ilabelled albumin showed a red cell mass of 35 ml/kg (normal range 30±5 ml/kg), and a plasma volume of 32-5 ml/kg (normal range 45±5 ml/kg); these indicated a relative polycythaemia, the raised haemoglobin level being mainly secondary to a reduction in plasma volume. Other findings included a leucocyte alkaline phosphatase score of 80 IU/1, serum B12 225 ng/l, serum folate 5-9 ,ug/l, red cell folate 304 [Lg/l, serum iron 23-3 ,umol/l (130 ,ug/100 ml), and TIBC 73 0 umol/l (408 Qug/100 ml). There was thus no evidence of any myeloproliferative disorder or deficiency state which could have held down the red cell mass. Bone marrow examination was refused. Intravenous pyelogram showed a small radio-opaque calculus at the lower pole of the left kidney, but no cause was found for this.The oxygen dissociation curve of the patient's whole blood measured by tonometry at pH 7-4 and 37'C (fig 1) was shifted to the left of that of a normal control, which indicated a raised oxygen affinity. The P50 (partial pressure of oxygen at which the haemoglobin is 50% saturated with oxygen) was 24 kPa (18 mm Hg) on two separate occasions (normal 3-6±0-2 kPa (27±1-5 mm Hg)). Arterial blood analysis was normal and showed a pH of 7-45, oxygen pressure (Po2) of 10 7 kPa (80 mm Hg), carbon dioxide pressure (Pco2) of 5-1 kPa (38 mm Hg), and an oxygen saturation of 9700. The carboxy haemoglobin level was 4 5%. The 2, 3-diphosphoglycerate (2,3-DPG) level, measured by a modification of the method of Lowry et al,2 was 8-5 ,umol/g haemoglobin (2-3 mg/g), which was at the lower end of the normal range of 8 2-17-4 ,umol/g-haemoglobin (2-2-4-6 mg/g). The oxygen affinity of the haemolysate was also increased when measured by the method of Imai3 at 20°C in 01-M potassium phosphate at five different pH values (fig 2). The P50 was about 830% of the value of a normal haemolysate but the Hill coefficient, n, and the alkaline Bohr effect were normal.

Hemoglobin Rahere, a human hemoglobin variant with amino acid substitution at the 2,3-diphosphoglycerate binding site. Functional consequences of the alteration and effects of bezafibrate on the oxygen bindings.

“…It was apparent that normal #T9 and ,BT10 peptides were absent in the peptide chromatograms, while three new peptides, (3T8/9/10, (3T9/10, and (3T9/I0/1 1, were found, each corre- from these results that the substitution must be a threonine residue for a lysine residue at position 82 of the 13-chains. This variant, therefore, is identical with hemoglobin Rahere that has been found in an English family by Lorkin et al (5). Oxygen equilibria.…”

“…Electrophoresis of hemolysates detected a hemoglobin variant, subsequently identified as hemoglobin Rahere (5), that migrated anodally to hemoglobin A at pH 8.6. Electrophoretic mobility of the variant on a cellulose acetate sheet was +3.07 at pH 8.6, measured by the method of Schneider and Barwick (12).…”

“…Since the discovery of the role of 2,3-diphosphoglycerate (DPG)' in regulating oxygen transport (1,2) led to the identification of the binding sites ofanionic cofactors in the hemoglobin molecule (3,4), an understanding of linkage between oxygen binding and cofactor binding has been sought through studies on hemoglobin variants with alterations at the 2,3-DPG binding site (5)(6)(7)(8)(9). Recently Perutz and Poyart (10) reported that low molecular weight compounds, such as 2-(4-chlorophenoxy)-2-methylpropionic acid (clofibric acid) and 2-[4-(2-p-chlorobenzamidethyl)-phenoxy]-2-methylpropionic acid (bezafibrate), have the remarkable ability to modify hemoglobin function in erythrocytes, a finding that opened the way to studies ofthe molecular control of hemoglobin function and its clinical application.…”

Oxygen Affinity of Hemoglobin in Polycythemia of Undetermined Etiology

“…Lorkin et al [2] described a patient with relative polycythemia and an abnormal he moglobin, characterized by an unusually high oxygen affinity: according to them it is worthwhile to determine the oxygen affinity of hemoglobin in patients with relative poly cythemia of undetermined etiology.…”

Hemoglobin Variants: Biochemical Properties and Clinical Correlates

“…Several high affinity Hb variants are caused by substitutions that inhibit interaction with 2,3DPG, which normally binds globin chains to stimulate O 2 release (Fig. 2C) invariant lysine in the 2,3DPG binding site of b globin, thereby reducing the affinity for this allosteric regulator (Lorkin et al 1975;Sugihara et al 1985). Several low affinity variants involve replacements at the a1b2 interface, which plays an important role in Hb cooperativity.…”