The inhibitory effect of benzenethiol on the cresolase and catecholase activities of mushroom tyrosinase |
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Authors: | A. A. Saboury S. Zolghadri K. Haghbeen A. A. Moosavi-Movahedi |
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Affiliation: | 1. Institute of Biochemistry and Biophysics, University of Tehran, Tehran, Iran;2. The National Research Center for Genetic Engineering and Biotechnology, Tehran, Iran |
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Abstract: | The inhibitory effect of benzenethiol on the cresolase and catecholase activities of mushroom tyrosinase (MT) have been investigated at two temperatures of 20 and 30°C in 10 mM phosphate buffer solution, pHs 5.3 and 6.8. The results show that benzenethiol can inhibit both activities of mushroom tyrosinase competitively. The inhibitory effect of benzenethiol on the cresolase activity is more than the catecholase activity of MT. The inhibition constant (Ki) value at pH 5.3 is smaller than that at pH 6.8 for both enzyme activities. However, the Ki value increases in cresolase activity and decreases in catecholase activity due to the increase of temperature from 20 to 30°C at both pHs. Moreover, the effect of temperature on Ki value is more at pH 6.8 for both cresolase and catecholase activities. The type of binding process is different in the two types of MT activities. The binding process for catecholase inhibition is only entropy driven, which means that the predominant interaction in the active site of the enzyme is hydrophobic, meanwhile the electrostatic interaction can be important for cresolase inhibition due to the enthalpy driven binding process. Fluorescence and circular studies also show a minor change in the tertiary structure, without any change in the secondary structure, of the enzyme due to the electrostatic interaction in cresolase inhibition by benzenethiol at acidic pH. |
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Keywords: | Mushroom tyrosinase benzenethiol competitive inhibition inhibition constant fluorescence circular dichroism |
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