Lack of allosterically controlled intramolecular transfer of nitric oxide from the heme to cysteine in the beta subunit of hemoglobin.
The SNO-Hb hypothesis holds that heme-bound nitric oxide (NO) present in the beta subunits of T-state hemoglobin (Hb) will be transferred to the beta-93 cysteine upon conversion to R-state Hb, thereby forming SNO-Hb. A deficiency in the ability of Hb to facilitate this intramolecular transfer has recently been purported to play a role in pulmonary hypertension and sickle cell disease. We prepared deoxygenated Hb samples with small amounts of heme-bound NO and then oxygenated the samples. Electron paramagnetic resonance (EPR) spectroscopy was used to (1) determine the concentration of iron nitrosyl Hb (Fe-NO Hb), (2) show that the NO is evenly distributed among alpha and beta subunits, and (3) show that the Hb undergoes a change in its quaternary state (T to R) upon oxygenation. We did not observe a decrease in the concentration of Fe-NO Hb on oxygenation, which is inconsistent with the prediction of the SNO-Hb hypothesis.
Huang
Kris T
KT
Department of Biomedical Engineering, Wake Forest University, Winston-Salem, NC 27109, USA.
Azarov
Ivan
I
Basu
Swati
S
Huang
Jinming
J
Kim-Shapiro
Daniel B
DB
D000328:Adult; D000494:Allosteric Regulation; D001692:Biological Transport; D003545:Cysteine / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D009569:Nitric Oxide / Q000378:metabolism*; D010108:Oxyhemoglobins / Q000378:metabolism; D021122:Protein Subunits
D006454:Hemoglobins; D010108:Oxyhemoglobins; D021122:Protein Subunits; D009569:Nitric Oxide; D006418:Heme; D003545:Cysteine