Non-Essential Activation of Co²⁺and Zn²⁺on Mushroom Tyrosinase: Kinetic and Structural Stability

Abstract

Tyrosinase is a widespread enzyme with great promising capabilities. The Lineweaver-Burk plots of the catecholase reactions showed that the kinetics of mushroom tyrosinase (MT), activated by Co 2+ and Zn 2+ at different pHs (6, 7, 8 and 9) obeyed the non-essential activation mode. The binding of metal ions to the enzyme increases the maximum velocity of the enzyme due to an increase in the enzyme catalytic constant (k cat ). From the kinetic analysis, dissociation constants of the activator from the enzyme-metal ion complex (K a ) were obtained as 5 × 10 4 M −1 and 8.33 × 10 3 M −1 for Co 2+ and Zn 2+ at pH 9 and 6 respectively. The structural analysis of MT through circular dichroism (CD) and intensive fluorescence spectra revealed that the conformational stability of the enzyme in these pHs reaches its maximum value in the presence of each of the two metal ions.

Investigation and Characterisation of New Eco-Friendly Cosmetic Ingredients Based on Probiotic Bacteria Ferment Filtrates in Combination with Alginite Mineral

“…According to the presented results, instead of inhibition by alginate through removal of necessary ions, alginite rathe released metal ions into the assay mixture, resulting in enhanced tyrosinase activity. On the other hand, alginite also has many metal ions [38] that contribute to the functioning of the enzyme, such as Co 2+ , Zn 2+ and Cu 2+ [39,40]. According to the presented results, instead of inhibition by alginate through removal of necessary ions, alginite rather released metal ions into the assay mixture, resulting in enhanced tyrosinase activity.…”

“…Humic acid can probably bind copper ions similarly (Figure 7). On the other hand, alginite also has many metal ions [38] that contribute to the func tioning of the enzyme, such as Co 2+ , Zn 2+ and Cu 2+ [39,40]. According to the presented results, instead of inhibition by alginate through removal of necessary ions, alginite rathe released metal ions into the assay mixture, resulting in enhanced tyrosinase activity.…”

Enzyme Modification and Oxidative Cross‐linking Using Carboxylate‐, Phenol‐ and Catechol‐Conjugated 1,8‐Naphthalimides

“…That study suggested the conformation change was induced by hydrophobic interactions between the histidine and methionines in the entrance to the active site, making the binding to L-dopa more favorable and inhibiting tyrosine oxidation (33). Current literature also suggests that the activation of mushroom tyrosinase by detergents, metal ions, oligopeptides and catechol-based (substrate) compounds is due to binding of copper ions within the active site that alter the structure and mechanism of oxidation (49)(50)(51)(52). Due to the similarities in enzyme kinetics between the naphthalimides and aarbutin, we conclude that the phenol group of the naphthalimides interacts with the active site and modifies the residues.…”