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Title: Density functional theory calculations on biological S-transfer: Insight into the mechanism of rhodanese
Authors: Dey, Subal
Dey, Abhishek
Keywords: Density functional calculations
S-transfer reactions
Cyanide detoxification
Issue Date: Sep-2011
Publisher: NISCAIR-CSIR, India
Abstract: Biological sulfur transfer (S-transfer) is a key step in the synthesis of metabolites, CN<sup>-</sup> detoxification and assembly of iron-sulfur clusters. Computational results addressing the thermodynamics of the S-transfer reactions from thiosulfate (natural S-donor) to HCN and thiol are presented. These calculations indicate that S-transfer from thiosulfate to HCN and thiol is possible only in the anionic forms of these species. However these species have <i style="">pK</i><sub>a</sub> values significantly higher than physiological <i style="">p</i>H value (i.e., they are protonated in physiological <i style="">p</i>H and incapable of S-transfer). In the rhodanese active site, basic residues are present to deprotonate the catalytic cysteine group which accepts the S-atom from thiosulfate. The resultant perthiol species transfer S-atom to CN<sup>-</sup> in a synchronous S-atom and H<sup>+</sup> transfer step facilitated by the two arginine residues present in the rhodanese active site.&nbsp; Based on these calculations, a mechanism is proposed for the rhodanese catalyzed CN<sup>-</sup> detoxification pathway.
Description: 1457-1462
ISSN: 0975-0975(Online); 0376-4710(Print)
Appears in Collections:IJC-A Vol.50A(09-10) [September-October 2011]

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