Dye-decolorizing peroxidase of Thermobifida halotolerance displays complex kinetics with both substrate inhibition and apparent positive cooperativity

Arch Biochem Biophys. 2024 Feb 19:109931. doi: 10.1016/j.abb.2024.109931. Online ahead of print.ABSTRACTDye-decolorizing peroxidases (DyPs) have been intensively investigated for the purpose of industrial dye decolorization and lignin degradation. Unfortunately, the characterization of these peroxidases is hampered by their non-Michaelis-Menten kinetics, exemplified by substrate inhibition and/or positive cooperativity. Although often observed, the underlying mechanisms behind the unusual kinetics of DyPs are poorly understood. Here we studied the kinetics of the oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), hydroquinones, and anthraquinone dyes by DyP from the bacterium Thermobifida halotolerans (ThDyP) and solved its crystal structure. We also provide rate equations for different kinetic mechanisms explaining the complex kinetics of heme peroxidases. Kinetic studies along with the analysis of the structure of ThDyP suggest that the substrate inhibition is caused by the non-productive binding of ABTS to the enzyme resting state. Strong irreversible inactivation of ThDyP by H2O2 in the absence of ABTS suggests that the substrate inhibition by H2O2 may be caused by the non-productive binding of H2O2 to compound I. Positive cooperativity was observed only with the oxidation of ABTS but not with the two electron-donating substrates. Although the conventional mechanism of cooperativity cannot be excluded, we propose that the oxidation of ABTS assumes...

Source: Archives of Biochemistry and Biophysics - February 21, 2024 Category: Biochemistry Authors: Hegne Pupart Tiit Lukk Priit V äljamäe Source Type: research