Kinetics and mechanism of formation of S-nitrosocysteine
The kinetics and mechanism of the nitrosation of cysteine by nitrous acid has been studied in acidic medium. The stoichiometry of the reaction is strictly 1:1, with the formation of one mole of S-nitrosocysteine (CySNO) from one mole of nitrous acid. Only two nitrosating agents were detected: nitrous acid itself and protonated nitrous acid which is the hydrated form of the nitrosonium cation, NO+. Nitric oxide itself was not detected as a nitrosant. The bimolecular rate constant for the direct nitrosation of cysteine by nitrous acid was determined to be 6.4 ± 1.1 L mol-1 s-1, while nitrosation by the nitrosonium cation has a rate constant of 6.8 x 10³ L mol-1 s-1. CySNO is short-lived, and decomposes completely to cystine and nitric oxide within 100 s in the presence of micromolar quantities of Cu(II) ions. Since the physiological environment contains many metal ions and metalloenzymes, it is unlikely that CySNO will be an effective carrier of NO.
| Main Authors: | , , |
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| Format: | Digital revista |
| Language: | English |
| Published: |
The South African Chemical Institute
2010
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| Online Access: | http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0379-43502010000100034 |
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| Summary: | The kinetics and mechanism of the nitrosation of cysteine by nitrous acid has been studied in acidic medium. The stoichiometry of the reaction is strictly 1:1, with the formation of one mole of S-nitrosocysteine (CySNO) from one mole of nitrous acid. Only two nitrosating agents were detected: nitrous acid itself and protonated nitrous acid which is the hydrated form of the nitrosonium cation, NO+. Nitric oxide itself was not detected as a nitrosant. The bimolecular rate constant for the direct nitrosation of cysteine by nitrous acid was determined to be 6.4 ± 1.1 L mol-1 s-1, while nitrosation by the nitrosonium cation has a rate constant of 6.8 x 10³ L mol-1 s-1. CySNO is short-lived, and decomposes completely to cystine and nitric oxide within 100 s in the presence of micromolar quantities of Cu(II) ions. Since the physiological environment contains many metal ions and metalloenzymes, it is unlikely that CySNO will be an effective carrier of NO. |
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