Intermediates Detected by Visible Spectroscopy during the Reaction of Nitrite with Deoxyhemoglobin: The Effect of Nitrite Concentration and Diphosphoglycerate

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• 作者：Enika Nagababu ; Somasundaram Ramasamy ; Joseph M. Rifkind
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：October 16, 2007
• 年：2007
• 卷：46
• 期：41
• 页码：11650 - 11659
• 全文大小：192K
• 年卷期：v.46,no.41(October 16, 2007)
• ISSN：1520-4995

文摘

The reaction of nitrite with deoxyhemoglobin (deoxyHb) results in the reduction of nitrite toNO, which binds unreacted deoxyHb forming Fe(II)-nitrosylhemoglobin (Hb(II)NO). The tight bindingof NO to deoxyHb is, however, inconsistent with reports implicating this reaction with hypoxic vasodilation.This dilemma is resolved by the demonstration that metastable intermediates are formed in the course ofthe reaction of nitrite with deoxyHb. The level of intermediates is quantitated by the excess deoxyHbconsumed over the concentrations of the final products formed. The dominant intermediate has a spectrumthat does not correspond to that of Hb(III)NO formed when NO reacts with methemoglobin (MetHb), butis similar to metHb resulting in the spectroscopic determinations of elevated levels of metHb. It is adelocalized species involving the heme iron, the NO, and perhaps the -93 thiol. The putative role for redcell reacted nitrite on vasodilation is associated with reactions involving the intermediate. (1) Theintermediate is less stable with a 10-fold excess of nitrite and is not detected with a 100-fold excess ofnitrite. This observation is attributed to the reaction of nitrite with the intermediate producing N₂O₃. (2)The release of NO quantitated by the formation of Hb(II)NO is regulated by changes in the distal hemepocket as shown by the 4.5-fold decrease in the rate constant in the presence of 2,3-diphosphoglycerate.The regulated release of NO or N₂O₃ as well as the formation of the S-nitroso derivative of hemoglobin,which has also been reported to be formed from the intermediates generated during nitrite reduction,should be associated with any hypoxic vasodilation attributed to the RBC.