Thiols heme, reaction with

The spontaneous reaction of nitric oxide with thiols is slow at physiological pH and the final product under anaerobic conditions is not a nitrosothiol (Pryor et al., 1982). The reaction is slow because it involves the conjugate base of the thiol (R—S"). At pH 7.0, the oxidation of cysteine by nitric oxide required 6 hr to reach completion and yields RSSR and N 2O as the products. The synthetic preparation of nitrosothiols usually involves the addition of nitrosonium ion from acidified nitrite to the thiol, or oxidation of the thiol with nitrogen dioxide under anaerobic conditions in organic solvents. Nitric oxide will form nitrosothiols by reaction with ferric heme groups, such as found in metmyoglobin or methemoglobin (Wade and Castro, 1990). It is also possible that nitrosyldioxyl radical also reacts with thiols to form a nitrosothiol. 

Chapters 11,18). It binds to the iron of heme groups in either the Fe or Fe " form and also reacts with thiol groups of proteins and small molecules to form S-nitrosothiols (R-S-N=0). It reacts with the heme iron of myoglobin and hemoglobin and, by transfer of one electron, can oxidize the iron of hemoglobin to the Fe + methemoglobin with formation of the nitroxyl ion NO This reaction may be a... 

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