Measurements of nitric oxide on the heme iron and beta-93 thiol of human hemoglobin during cycles of oxygenation and deoxygenation. Proc Natl Acad Sci U S A 2003 Sep 30;100(20):11303-8
Date
09/23/2003Pubmed ID
14500899Pubmed Central ID
PMC208752DOI
10.1073/pnas.2033883100Scopus ID
2-s2.0-0141594579 (requires institutional sign-in at Scopus site) 78 CitationsAbstract
Nitric oxide has been proposed to be transported by hemoglobin as a third respiratory gas and to elicit vasodilation by an oxygen-linked (allosteric) mechanism. For hemoglobin to transport nitric oxide bioactivity it must capture nitric oxide as iron nitrosyl hemoglobin rather than destroy it by dioxygenation. Once bound to the heme iron, nitric oxide has been reported to migrate reversibly from the heme group of hemoglobin to the beta-93 cysteinyl residue, in response to an oxygen saturation-dependent conformational change, to form an S-nitrosothiol. However, such a transfer requires redox chemistry with oxidation of the nitric oxide or beta-93 cysteinyl residue. In this article, we examine the ability of nitric oxide to undergo this intramolecular transfer by cycling human hemoglobin between oxygenated and deoxygenated states. Under various conditions, we found no evidence for intramolecular transfer of nitric oxide from either cysteine to heme or heme to cysteine. In addition, we observed that contaminating nitrite can lead to formation of iron nitrosyl hemoglobin in deoxygenated hemoglobin preparations and a radical in oxygenated hemoglobin preparations. Using 15N-labeled nitrite, we clearly demonstrate that nitrite chemistry could explain previously reported results that suggested apparent nitric oxide cycling from heme to thiol. Consistent with our results from these experiments conducted in vitro, we found no arterial/venous gradient of iron nitrosyl hemoglobin detectable by electron paramagnetic resonance spectroscopy. Our results do not support a role for allosterically controlled intramolecular transfer of nitric oxide in hemoglobin as a function of oxygen saturation.
Author List
Xu X, Cho M, Spencer NY, Patel N, Huang Z, Shields H, King SB, Gladwin MT, Hogg N, Kim-Shapiro DBAuthor
Neil Hogg PhD Associate Dean, Professor in the Biophysics department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
HemeHemoglobins
Humans
Iron
Nitric Oxide
Oxygen
