Effects of S-nitrosation on oxygen binding by normal and sickle cell hemoglobin.
S-Nitrosated hemoglobin (SNO-Hb) is of interest because of the allosteric control of NO delivery from SNO-Hb made possible by the conformational differences between the R- and T-states of Hb. To better understand SNO-Hb, the oxygen binding properties of S-nitrosated forms of normal and sickle cell Hb were investigated. Spectral assays and electrospray ionization mass spectrometry were used to quantify the degree of S-nitrosation. Hb A(0) and unpolymerized Hb S exhibit similar shifts toward their R-state conformations in response to S-nitrosation, with increased oxygen affinity and decreased cooperativity. Responses to 2, 3-diphosphoglycerate were unaltered, indicating regional changes in the deoxy structure of SNO-Hb that accommodate NO adduction. A cycle of deoxygenation/reoxygenation does not cause loss of NO or appreciable heme oxidation. There is, however, appreciable loss of NO and heme oxidation when oxygen-binding experiments are carried out in the presence of glutathione. These results indicate that the in vivo stability of SNO-Hb and its associated vasoactivity depend on the abundance of thiols and other factors that influence transnitrosation reactions. The increased oxygen affinity and R-state character that result from S-nitrosation of Hb S would be expected to decrease its polymerization and thereby lessen the associated symptoms of sickle cell disease.
Bonaventura
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Duke University Marine Biomedical Center, Nicholas School of the Environment Marine Laboratory, Beaufort, North Carolina 28516, USA. bona@duke.edu
Ferruzzi
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Tesh
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Stevens
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RD
D000494:Allosteric Regulation; D000838:Anions / Q000494:pharmacology; D003545:Cysteine / Q000737:chemistry; D005978:Glutathione / Q000494:pharmacology; D006441:Hemoglobin A / Q000737:chemistry*; D006451:Hemoglobin, Sickle / Q000737:chemistry*; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D013058:Mass Spectrometry; D008706:Methemoglobin / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry*; D011485:Protein Binding; D013053:Spectrophotometry; D013438:Sulfhydryl Compounds / Q000494:pharmacology
D000838:Anions; D006451:Hemoglobin, Sickle; D006454:Hemoglobins; C103574:S-nitrosohemoglobin; D013438:Sulfhydryl Compounds; C028881:hemoglobin A(0); D008706:Methemoglobin; D006441:Hemoglobin A; D005978:Glutathione; D003545:Cysteine; D010100:Oxygen