The hemoglobin of amphibia

Hemoglobin can nitrate itself and other proteins

Incubation of human hemoglobin with nitrite and hydrogen peroxide was found to induce autonitration and nitration of another protein (bovine serum albumin), as demonstrated by detection of nitrotyrosine residues in Western blots of separated membrane proteins. Inhibition of nitration by conversion of hemoglobin into the cyanmet form demonstrates that nitration is due to the pseudoperoxidase activity of hemoglobin. Incubation of whole erythrocytes with nitrite and hydrogen peroxide induces nitration of erythrocyte membrane proteins, much stronger when cellular catalase was inhibited with azide. These results suggest that hemoglobin and other hemoproteins may contribute to the tyrosine nitration in vivo.

The effects of in vivo and in vitro non-enzymatic glycosylation and glycoxidation on physico-chemical properties of haemoglobin in control and diabetic patients

The erythrocyte deformability, which is related to erythrocyte internal viscosity, was suggested to depend upon the physico-chemical properties of haemoglobin. In the present study we employed ESR spectroscopy on order to explore further the extent to which the in vivo or in vitro glycation and/or glycoxidation might affect haemoglobin structure on conformation. We revealed that under both in vivo and in vitro conditions the attachment of glucose induced a mobilization of thiol groups in the selected domains of haemoglobin molecules ( the increased h+1/h0 parameter of maleimide spin label, MSL; 0.277 +/- 0.021 in diabetics vs 0.338 +/- 0.017 in controls, n = 12, P < 0.0001). The relative rotational correlation time (tau c) of two spin labels, TEMPONE and TEMPAMINE, respectively, in erythrocyte insides (5.22 +/- 0.42 in diabetics, n = 21 vs 4.79 +/- 0.38, n = 16 in controls, P < 0.005) and in the solutions of in vitro glycated haemoglobin, were increased. Neither oxidation nor crosslinking of thiol groups was evidenced in glycated and/or oxidized haemoglobin. In addition, erythrocyte deformability was found to be reduced in type 2 diabetic patients (6.71 +/- 1.08, n = 28 vs 7.31 +/- 0.96, n = 21, P < 0.015). In conclusion, these observations suggest that: the attachment of glucose to haemoglobin might have decreased the mobility of the Lys-adjacent Cys residues, thus leading to the increased h+1/h0 parameter of MSL. Such structural changes in haemoglobin owing to non-enzymatic glycosylation may contribute to the increased viscosity of haemoglobin solutions (r = 0.497, P < 0.0035) and the enhanced internal viscosity of diabetic erythrocytes (r = 0.503, P < 0.003). We argue that such changes in haemoglobin, and consequently in red blood cells, might contribute to the handicapped oxygen release under tissue hypoxia in the diabetic state.

Direct evidence for the alterations in protein structure and conformation upon in vitro nonenzymatic glycosylation

The formation of nonenzymatic glycosylation products appears to be a link between chronic hyperglycaemia and long-term diabetic complications. However, little is known concerning the glycation-induced modifications in the structure and conformation of proteins, which possibly underlie their altered functional characteristics. This study conveys a direct evidence for and compares the glucose-induced modifications in the conformation of three proteins with various half-lives: bovine serum albumin, human haemoglobin and bovine tendon collagen. These proteins incubated in vitro with glucose in various media containing optionally EDTA and Fe2+ ions contained up to 4-10 times as much attached glucose as did their relevant controls, and the extent of glycation was the highest in the samples incubated under air or in the absence of EDTA. The fluorescence and ESR data indicate that the Trp in albumin molecule, given albumin glycation-induced structural modifications, became more exposed to water surrounding solution whereas the Trp residues of haemoglobin remained shielded from water; also collagen fluorescence derived from the supposedly newly formed covalent crosslinks is vastly increased, and particularly when collagen was glycated under air or in the presence of Fe2+ ions. Possible mechanisms underlying the increased mobility of selected protein domains and glycation-mediated alterations in protein conformation are considered and discussed.

Consequences of the presence of elongated variant of the major transmembrane protein (Band 3 protein) in the human erythrocyte

Among 56 persons studied, 6 were heterozygous with respect to the elongated variant of the Band 3 protein (anion transporting protein) of the erythrocyte membranes. Erythrocytes containing the variant Band 3 protein did not exhibit morphologic abnormalities, alterations in electron spin resonance spectra of maleimide-spin labeled membranes. In the rate of membrane 'self-digestion' or in chloride permeability. They did however show an increased membrane binding of hemoglobin and aldolase.

Les hemoglobines des amphibiens: Separation et caracterisation preliminaire des chaines d'une hemoglobine du crapaud bufo bufo

A toad (Bufo bufo) hemoglobin has been purified and two types of chain have been separated by counter-current distribution. The alpha-chain has a N-terminal sequence Ac-Ala-Leu and a C-terminal sequence Tyr-Arg. The beta-chain has a N-terminal sequence Val-His-Leu and a C-terminal sequence Tyr-His.