Volume 17, Issue 86 (5-2010)                   Daneshvar Medicine 2010, 17(86): 27-36 | Back to browse issues page

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gheibi N, sirati sabet M. The effect of cobalt on the kinetic and structure of mushroom tyrosinase. Daneshvar Medicine. 2010; 17 (86) :27-36
URL: http://daneshvarmed.shahed.ac.ir/article-1-26-en.html
Abstract:   (7727 Views)

  Background & Objective : Tyrosinase is a widespread enzyme with great promising capabilities. Its outstanding role has to be addressed with considering kinetic, structure and stability issues. Comprehensive kinetics studies on both cresolase and catecholase activities of mushroom tyrosinase (MT) resulted in elucidation of complicated enzyme kinetics. Yet some important aspects of the enzyme structure, mechanism, and behavior have been unresolved. The aim of this study was To determine the effect of cobalt on the kinetic and structure of mushroom tyrosinase.

 

  Materials and Methods: This study devoted to explore the MT structure through circular dichroism (CD) and spectroflourimetric techniques. Its true kinetics assessed in the presence of caffeic as substrate and Co2+ in different pHs 6, 7, 8 and 9.

 

  Results: Kinetic of MT activation with this metal ion was obeyed from non-essential activation of an enzyme by an activator molecule . Then, the slope and Y-intercept changes in the Lineweaver-Burk plot due to the presence of metal at different concentration are obtained and replotted their inverse vs. inverse concentration of the activator as the secondary plot to find α, β and KA values. The α value (α < 1) obtained herein suggests that the binding of the ion to the enzyme can increase the binding affinity of the substrate. The β value (β>1) obtained also suggests that the binding of metal ion to the enzyme can increase the maximum velocity of the enzyme due to the increase of the enzyme catalytic constant (kcat). The optimum activity of the enzyme without the presence of metal ions was carried out in pH=7.

 

  Conclusion: Conformational changes of the enzyme through the measurements of its secondary and tertiary structures by CD and fluorescence spectroscopic studies , respectively showed enzyme stability due to the structural changes for Co2+ in pH 9. It is concluded that with this transitional metal ion kinetic pathway of activation follows the general non-essential activation system and its binding may be close enough to the binuclear centre to interact allosterically with the substrate binding site . Besides, the enzyme optimum activity not occurred in its optimum stability.

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