PubMed · 7186427
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P R Sohmer, R L Scott. 1982. Massive transfusion.. https://pubmed.ncbi.nlm.nih.gov/7186427/
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IMP was found to activate AMP deaminase in crude glucose-depleted human erythrocyte lysates. Activation of the enzyme by IMP is due to prevention of the inhibitory effect of inorganic phosphate. At 1 mM AMP and 2-3 mM phosphate the addition of 2-5 mM IMP accelerates the AMP deamination two to three times.
It is generally believed that bovine hemoglobin (BvHb) interacts weakly with 2,3-diphosphoglycerate (2,3-DPG) in a chloride-free media and not at all in the presence of physiological concentrations of chloride (100 mM). This lack of interaction has raised several questions at both structural and evolutionary levels. Results obtained in this study via 31P nuclear magnetic resonance (NMR) show that, even in the presence of 100 mM chloride ions, 2,3-DPG does, in fact, interact with bovine deoxy-Hb. This spectroscopic observation has been confirmed by oxygen binding experiments, which have also shown that, under certain conditions, chloride and 2,3-DPG may display a synergistic effect in modifying the oxygen affinity of bovine hemoglobin. It could be that this synergistic effect has its structural basis in a conformational modification induced by 2,3-DPG, possibly causing extra chloride anions to approach the positive charges which constitute the anion binding site. Another possibility, not necessarily an alternative, is the additional chloride binding site recently identified [Fronticelli, C., Sanna, M. T., Perez-Alvarado, G. C., Karavitis, M., Lu, A.-L., and Brinnigar, W. S. (1995) J. Biol. Chem 270, 30588-30592] involving lysine beta76 that in bovine Hb substitutes for the alanine residue present in human hemoglobin. All of these findings are in agreement with the very low enthalpy of oxygenation that characterizes bovine Hb when both chloride and 2,3-DPG are present in concomitance. The results reported here clearly show that bovine hemoglobin does react with 2, 3-DPG and is functionally affected by this organic phosphate. Hence, the very low intraerythrocytic concentration of 2,3-DPG (0.5 mM) in adult bovine red blood cells is the result of metabolic adaptation which cannot be explained solely by the different amino acid sequence at the level of the 2,3-DPG binding site.
alpha-Nitrosyl hemoglobin, alpha(Fe-NO)2beta(Fe)2, which is frequently observed upon reaction of deoxy hemoglobin with limited quantities of NO in vitro as well as in vivo, has been synthetically prepared, and its reaction with O2 has been investigation by EPR and thermodynamic equilibrium measurements. alpha-Nitrosyl hemoglobin is relatively stable under aerobic conditions and undergoes reversible O2 binding at the heme sites of its beta-subunits. Its O2 binding is coupled to the structural/functional transition between T- (low affinity extreme) and R- (high affinity) states. This transition is linked to the reversible cleavage of the heme Fe-proximal His bonds in the alpha(Fe-NO) subunits and is sensitive to allosteric effectors, such as protons, 2,3-biphosphoglycerate, and inositol hexaphosphate. In fact, alpha(Fe-NO)2beta(Fe)2 is exceptionally sensitive to protons, as it exhibits a highly enhanced Bohr effect. The total Bohr effect of alpha-nitrosyl hemoglobin is comparable to that of normal hemoglobin, despite the fact that the oxygenation process involves only two ligation steps. All of these structural and functional evidences have been further confirmed by examining the reactivity of the sulfhydryl group of the Cysbeta93 toward 4, 4'-dipyridyl disulfide of several alpha-nitrosyl hemoglobin derivatives over a wide pH range, as a probe for quaternary structure. Despite the halved O2-carrying capacity, alpha-nitrosyl hemoglobin is fully functional (cooperative and allosterically sensitive) and could represent a versatile low affinity O2 carrier with improved features that could deliver O2 to tissues effectively even after NO is sequestered at the heme sites of the alpha-subunits. It is concluded that the NO bound to the heme sites of the alpha-subunits of hemoglobin acts as a negative allosteric effector of Hb and thus might play a role in O2/CO2 transport in the blood under physiological conditions.