title: Oxygen equilibrium curve shape and allohemoglobin interaction in sheep whole blood.
abstract: Adult sheep (Ovis aries) exhibit hemoglobin heterogeneity controlled by two autosomal alleles with codominant expression (Hb AA, AB, BB). Isoelectric points for Hb A and Hb B were 6.94 and 7.15, respectively; for Hb AB animals, the two allohemoglobins were present in equimolar concentrations (Hb A = 52%, Hb B = 48%). Dynamic O2 equilibrium curves (O2ECs) were generated for sheep whole blood at 39 degrees C using thin-film techniques. Half-saturation PO2 values (P50) at pH 7.50 were 31.3, 35.7, and 40.7 Torr for Hb AA, AB, and BB, respectively. CO2 Bohr coefficients at saturation (S) = 0.5 (delta log P50/delta pH) were similar for all phenotypes, ranging from -0.38 to -0.40. The Bohr slopes were also saturation independent between 0.2 and 0.8 S. Standard O2ECs for each phenotype were accurately fitted to three-constant third-order polynomial expressions. Sheep equilibrium curves were not isomorphic with other mammalian O2ECs (e.g., human and dog); sheep curves exhibited greater sigmoidicity. Furthermore, allohemoglobin interaction was not detected in heterozygous sheep. The blood O2 binding characteristics (P50, curve shape, and delta log PO2/delta pH) for Hb AB sheep and an experimental blood mixture containing equal proportions of Hb AA and Hb BB erythrocytes were equivalent.
mesh_terms: D000483:Alleles; D000818:Animals; D006441:Hemoglobin A / Q000032:analysis* / Q000235:genetics; D006444:Hemoglobin C / Q000032:analysis / Q000235:genetics; D006454:Hemoglobins / Q000032:analysis* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D008433:Mathematics; D010100:Oxygen / Q000097:blood*; D010108:Oxyhemoglobins / Q000378:metabolism; D010641:Phenotype; D012756:Sheep / Q000097:blood*
chemical_list: D006454:Hemoglobins; D010108:Oxyhemoglobins; D006444:Hemoglobin C; D006441:Hemoglobin A; C020622:hemoglobin B; D010100:Oxygen