Isoelectric focusing in gels

CO2produced within skeletal muscle has to leave the body finally via ventilation by the lung. To get there, CO2 diffuses from the intracellular space into the convective transport medium blood with...

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Carbon dioxide transport and carbonic anhydrase in blood and muscle

Recent improvements in the understanding of electrostatic interactions in proteins serve as a focus for the general topic of pH-dependent processes in proteins. The general importance of pH-dependent processes is first set out in terms of hydrogen ion equilibria, stability, ligand interactions, assembly, dynamics, and events in related molecular systems. The development of various theoretical treatments includes various formalisms in addition to the solvent interface model developed by Shire et al. as an extension of the Tanford-Kirkwood treatment. A number of detailed applications of the model are presented and future potentialities are sketched.

pH-dependent processes in proteins

Hemoglobin (Hb) constitutes a vital link between ambient O2 availability and aerobic metabolism by transporting oxygen (O2) from the respiratory surfaces of the lungs or gills to the O2-consuming tissues. The amount of O2 available to tissues depends on the blood-perfusion rate, as well as the arterio-venous difference in blood O2 contents, which is determined by the respective loading and unloading O2 tensions and Hb-O2-affinity. Short-term adjustments in tissue oxygen delivery in response to decreased O2 supply or increased O2 demand (under exercise, hypoxia at high altitude, cardiovascular disease, and ischemia) are mediated by metabolically induced changes in the red cell levels of allosteric effectors such as protons (H(+)), carbon dioxide (CO2), organic phosphates, and chloride (Cl(-)) that modulate Hb-O2 affinity. The long-term, genetically coded adaptations in oxygen transport encountered in animals that permanently are subjected to low environmental O2 tensions commonly result from changes in the molecular structure of Hb, notably amino acid exchanges that alter Hb's intrinsic O2 affinity or its sensitivity to allosteric effectors. Structure-function studies of animal Hbs and human Hb mutants illustrate the different strategies for adjusting Hb-O2 affinity and optimizing tissue oxygen supply.

Oxygen transport by hemoglobin.

To calculate cardiac output by the indirect Fick principle, CO2 concentrations (Cco 2) of mixed venous (CvCO2 ) and arterial blood are commonly estimated from Pco 2, based on the assumption that t...

https://www.physiology.org/doi/pdf/10.1152/jappl.2001.90.5.1798

Carbon dioxide pressure-concentration relationship in arterial and mixed venous blood during exercise

THE unloading of oxygen in the tissues is facilitated by lowering the oxygen affinity of haemoglobin (Hb) by both CO2 and diphosphoglycerate (DPG)1. This occurs because CO2 and DPG are oxygen-linked, that is, they are bound more firmly to deoxyhaemoglobin than to oxyhaemoglobin2,3. The binding of CO2 to Hb takes place by a reaction of CO2 with the α-amino groups to form carbamino compounds4,5, and binding curves can be measured by rather laborious methods4,6. Perrella et al.7 have modified these methods so that much smaller amounts of Hb, such as the specifically carbamylated Hbs8, can be used. In this method, Hb equilibrated with CO2 is rapidly taken to pH 11 to stabilise the carbamino CO2 and BioRad AG 1×8 resin added to remove carbonate and bicarbonate ions. The carbamino CO2 is displaced from the Hb by acidification and measured in a Van Slyke apparatus. DPG-free human deoxyhaemoglobin gave diphasic CO2 binding curves7 showing that the affinities of the α and β chain α-amino groups for CO2 are different, but it was impossible to establish which group had the higher affinity.

Identification of the high and low affinity CO2-binding sites of human haemoglobin.

IN paroxysmal nocturnal haemoglobinuria (PNH) a membrane abnormality renders the red blood cell (RBC) extremely sensitive to the lytic action of complement1. The nature of the abnormality is unknown: an alteration of the cell lipids has been postulated on the basis of the results of some lipid determinations2–8 and the greater tendency of lipids to form peroxides after exposure to ultraviolet light or H2O29–11. Alteration of the membrane proteins has also been proposed as the cause of the cell abnormality12,13. It has been found that treatment with some sulphydryl compounds renders normal RBCs similar to those in PNH in many respects14. In particular, they display a sensitivity to complement lysis twenty-fold greater than normal15 and have a very low acetylcholinesterase activity16. Among the sulphydryl compounds so far examined14,17–20 the radio-protector AET (2-amino-ethyl-isothiouronium bromide) has been shown to be the most effective in producing the PNH-like abnormality21. The PNH-like alteration induced in normal cells by sulphydryl compounds has not yet been identified, although it seems to involve the breaking of membrane disulphide bonds21. We have studied PNH and AET RBC membranes in parallel using sodium dodecyl sulphate (SDS) electrophoresis in Polyacrylamide gels. Our experiments show further similarities between PNH and AET cells and indicate that, in both, the alteration (or at least part of it) is located in the protein moiety of the membrane, where an abnormal polypeptide chain is demonstrable.

The membrane abnormality of the red cell in paroxysmal nocturnal haemoglobinuria.

Si e studiato se l'incubazione di emazie normali con una soluzione di GSSG addizionato di una piccola quantita di GSH fosse in grado di provocare in loro la lesione simil-EPN (emoglobinuria parossistica notturna). Si e osservato che questa in effetti si produce, probabilmente attraverso un meccanismo di scambio disolfurico tra i legami-S-S-della membrana eritrocitaria e quelli del GSSG, catalizzato da gruppi GS-.

M. Perrella

Papers

Identification of the high and low affinity CO2-binding sites of human haemoglobin.

The membrane abnormality of the red cell in paroxysmal nocturnal haemoglobinuria.

PNH-like red cells: Mechanism of action of sulfhydryl compounds on normal red cells