| Reactive sulfur species: kinetics and mechanism of the equilibrium between cysteine sulfenyl thiocyanate and cysteine thiosulfinate ester in acidic aqueous solution. | |
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MedLine Citation:
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PMID: 18351774 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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The kinetics and mechanism of the hydrolysis of cysteine sulfenyl thiocyanate (CySSCN) to give cysteine thiosulfinate ester (CyS(=O)SCy) have been investigated between pH 0 and 4. The reaction is reversible. The hydrolysis of CySSCN is second-order in [CySSCN] and inverse first-order in [H+] and [SCN-]. The following mechanism is proposed for the hydrolysis of CySSCN (where the charge depends upon the pH): CySSCN0/+ + H2O <==>CySOH0/+ + SCN- + H+, CySOH0/+ + CySSCN0/+ --> CyS(=O)SCy0/+/2+ + SCN- + H+; k1 = 3.36 +/- 0.01 x 10-3 s-1, K1k2 = 0.13 +/- 0.05 Ms-1 (which yields k2/k-1 = 39 M). The observed rate law rules out alternative mechanisms for 1 <or= pH <or= 4, including the condensation of two molecules of cysteine sulfenic acid (CySOH) to give CyS(=O)SCy. The equilibrium can be approached from the opposite direction. The reaction of CyS(=O)SCy with SCN- to give CySSCN is first-order in [CyS(=O)SCy], [SCN-], and [H+] (for [H+] > 0.4 M). The following mechanism is proposed: CyS(=O)SCy2+ + H+ <==> CyS(OH)=SCy3+, Ka; CyS(OH)SCy3+ + SCN- --> CySOH+ + CySSCN+, k-2 = 0.239 +/- 0.007 M-2s-1/Ka M-1. Since cysteine sulfenic acids are known to play an important function in many enzymes, and SCN- exists in abundance in physiologic fluids, we discuss the possible role of sulfenyl thiocyanates in vivo. |
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Authors:
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Kelemu Lemma; Michael T Ashby |
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Publication Detail:
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Type: Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, Non-P.H.S. Date: 2008-03-20 |
Journal Detail:
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Title: The Journal of organic chemistry Volume: 73 ISSN: 0022-3263 ISO Abbreviation: J. Org. Chem. Publication Date: 2008 Apr |
Date Detail:
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Created Date: 2008-04-11 Completed Date: 2008-06-09 Revised Date: - |
Medline Journal Info:
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Nlm Unique ID: 2985193R Medline TA: J Org Chem Country: United States |
Other Details:
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Languages: eng Pagination: 3017-23 Citation Subset: IM |
Affiliation:
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Department of Chemistry and Biochemistry, University of Oklahoma, Norman, Oklahoma 73019, USA. |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Acids
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chemistry* Cystine / chemistry* Esters / chemistry* Hydrogen-Ion Concentration Hydrolysis Kinetics Mercaptoethanol / chemistry Solutions Sulfur / chemistry* Thiocyanates / chemistry* Thiosulfonic Acids / chemistry* |
| Grant Support | |
ID/Acronym/Agency:
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1 R21 DE016889-01A2/DE/NIDCR NIH HHS |
| Chemical | |
Reg. No./Substance:
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0/Acids; 0/Esters; 0/Solutions; 0/Thiocyanates; 0/Thiosulfonic Acids; 302-04-5/thiocyanate; 56-89-3/Cystine; 60-24-2/Mercaptoethanol; 7704-34-9/Sulfur |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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