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Calorimetric Studies on the Interaction between two n-alkyl Xanthates and Mushroom Tyrosinase

Author Affiliations

  • 1Department of Chemistry, Imam Khomeini International University, Qazvin, IRAN
  • 2Department of Chemistry, Faculty of science, Islamic Azad University, Takestan branch, Takestan, IRAN
  • 3Institute of Biochemistry and Biophysics, University of Tehran, Tehran, IRAN

Res.J.chem.sci., Volume 2, Issue (9), Pages 90-92, September,18 (2012)

Abstract

Thermodynamics of the interaction between two iso-alkyl dithiocarbonates (xanthates), C3H7OCS2Na (I), C5H11OCS2Na (II) with mushroom tyrosinase was investigated at 27°C, pH 6.8 and in phosphate buffer (10 mM) by isothermal titration calorimetry to clarify thermodynamics of this binding as well as structural changes of the enzyme due to its interaction with xanthates. These compounds are potent inhibitors of MT with K values of 9.07 x 104, 1.68 x 105 M-1 for I and II, respectively. The MT inhibition is related to the chelating of the copper ions at the active site by a negative head group (S-) of the anion xanthate. Different Ka values for MT inhibition are related to different interactions of the aliphatic chains of I and II with hydrophobic pockets in the active site of the enzyme. The obtained results indicate that there are two identical and non-cooperative binding sites for both xanthates. The extended solvation theory was used to elucidate the effect of these xanthates on the stability of enzyme. These compounds are potent inhibitors of MT with association equilibrium constant (Ka) values of 9.0710 and 1.68×105 L.mol-1 for I and II, respectively. Different K values for MT inhibition are related to different interactions of the aliphatic chains of I and II with hydrophobic pockets in the active site of the enzyme. It is possible to ascribe the values of A and for I and II to the type of inhibition. The obtained results indicate that there are two identical and non-cooperative binding sites for both xanthates.

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