Hemoglobin-O2 affinity regulation: DPG, monovalent anions, and hemoglobin concentration

Abstract

The effects of organic (sodium benzoate derivatives) and inorganic (Cl-, I-, SCN-) anion concentration on O2 affinity (P50 [partial pressure of O2 at 50% Hb saturation, pH 7.4, 37.degree. C]) of Hb solutions obtained from adult human, cow and sheep blood were studied. An increase in dialyzed human adult Hb concentration from 0.89 to 4.78 mM at pH 7.1, PCO2 [partial pressure of CO2] 35-40 Torr, 37.degree. C, increased P50 from 7.8 .+-. 0.2 to 18.5 .+-. 0.6 Torr (mean .+-. SD). The rise in P50 produced by organic and inorganic anions depended on: nature of the anion, its concentration, and Hb concentration. Among organic anions, 2-iodosodium benzoate ([OISB] = 32 mM) increased P50 of adult human red blood cells (RBC''s) in Krebs-[HCO3-] at extracellular pH 7.4 from 24.9 .+-. 0.6 to 32.8 .+-. 1.7 Torr (mean .+-. SD) in the presence of noraml 2,3-diphosphoglyceric acid (2,3-DPG) concentrations while P50 of sheep RBC rose from 37.8 .+-. 1.1 to 52.7 .+-. 2.6 Torr. Although inorganic chloride (20 M/M Hb) and 2,3-DPG (1 M/M Hb) each increased P50 of concentrated (3.58 mM) sheep Hb solutions by 10-11 Torr, no additional effect was apparent with the combination. Ruminant Hb responded to 2,3-DPG, but this effect was obscured in the presence of Cl-. Equilibration of OISB between extra- and intracellular compartments was rapid and reversible after washing of RBC with saline. It did not produce hemolysis. The affinity-lowering properties of anions were not exclusively valence-dependent since monovalent bromothymol blue had a greater effect on P50 of Hb solutions than an equal concentration of 2,3-DPG.