The Influence of MgCl₂ on the O₂-Hb-Binding Curve of Human Hemoglobin Under Intracellular Conditions

Abstract

In 1969 a model was proposed (BARNIKOL et al.) to explain the effect of the Hb- concentration on the O₂- Hb- binding curve (GROTE, 1967). The existence of at least one low molecular substance (called Z) besides H and CO₂ was postulated, which is equimolar with Hb (≈ 5 mM) and which is bound preferentially to deoxy- Hb. From a simple stoichiometric consideration it follows, that a substance can only have a measurable influence on the O₂- Hb- binding curve, if its molar concentration is not to low compared with the molar Hb- concentration. For example, 2,3- diphosphogly-cerate (= DPG), glutathione and Mg⁺⁺ have intracellular concentrations of the necessary magnitude. Only a small part of Magnesium is bound to the membrane of the erythrocytes (HARRISON et al.). Principally all these substances are candidates for Z. In 1967 it was shown by BENESCH et al. and by CHANUTIN et al., that ATP and DPG influence the O₂-Hb- binding curve as was postulated for Z, and it was shown (BENESCH et al., 1968), that the organic phosphates are bound preferentially to deoxy-Hb. In our speculation on the chemical nature of Z first we prefered Mg⁺⁺ because of its complex forming properties. It is known for a long time, that Mg⁺⁺ forms a complex with ATP (MARTELL et al.,1956) and in 1970 it was found, that DPG forms also a complex with Mg⁺⁺ (COLLIER et al.).