Functional and subunit assembly properties of hemoglobin alberta ( α2β2101 Glu → Gly)

• Published in: Journal of molecular biology Vol. 183; no. 1; pp. 105 - 112
• Main Authors: McDonald, Melisenda J., Turci, Susan M., Bleichman, Margaret, Stinson, Robert A.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.01.1985
• ISSN: 0022-2836; 1089-8638
• DOI: 10.1016/0022-2836(85)90284-0

Hemoglobin Alberta has an amino acid substitution at position 101 (Glu → Gly), a residue involved in the α 1β 2 contact region of both the deoxy and oxy conformers of normal adult hemoglobin. Oxygen equilibrium measurements of stripped hemoglobin Alberta at 20 °C in the absence of phosphate revealed a high affinity ( P 50 = 0.75 mm Hg at pH 7), co-operative hemoglobin variant ( n = 2.3 at pH 7) with a normal Bohr effect ( −Δ log P 50 Δ pH 7 − 8 = 0.65 ). The addition of inositol hexaphosphate resulted in a decrease in oxygen affinity ( P 50 = 8.2 mm Hg at pH 7), a slight increase in the value of n and an enhanced Bohr effect. Rapid mixing experiments reflected the equilibrium results. A rapid rate of carbon monoxide binding ( l′ = 7.0 × 10 5m −1 s −1) and a slow rate of overall oxygen dissociation ( k = 15 s −1) was seen at pH 7 and 20 °C in the absence of phosphate. Under these experimental conditions the tetramer stability of liganded and unliganded hemoglobin Alberta was investigated by spectrophotometric kinetic techniques. The 4 K 4 value (the liganded tetramer-dimer equilibrium dissociation constant) for hemoglobin Alberta was found to be 0.83 × 10 −6m compared to a 4 K 4 value for hemoglobin A of 2.3 × 10 −6m, indicating that the Alberta tetramer was less dissociated into dimers than the tetramer of hemoglobin A. The values of 0 K 4 (the unliganded tetramer-dimer equilibrium dissociation constant) for hemoglobin Alberta and hemoglobin A were also measured and found to be 2.5 × 10 −8m and 1.5 × 10 −10m, respectively, demonstrating a greatly destabilized deoxyhemoglobin tetramer for hemoglobin Alberta compared to deoxyhemoglobin A. The functional and subunit dissociation properties of hemoglobin Alberta appear to be directly related to the dual role of the β101 residue in stabilizing the tetrameric form of the liganded structure, while concurrently destabilizing the unliganded tetramer molecule.