A case for myoglobin-macromolecular rate theory applied to pseudo peroxidase kinetics

This study explores the well-known catalytic behavior of myoglobin as a pseudo-peroxidase by applying macromolecular rate theory (MMRT) to assess its temperature-dependent enzyme kinetics. While myoglobin is primarily recognized for its oxygen-binding properties in muscle tissues, with a characterized pseudo-peroxidase ability to catalyze the degradation of hydrogen peroxide in the presence of electron donors, the claim that myoglobin is actually a true peroxidase can be explored by analyzing the heat capacity changes (ΔC_p ^‡) in the catalyzed reaction at different temperatures and fitting the results to the expanded Eyring equation (MMRT equation). This research uses the MMRT equation to compare myoglobin's catalytic activity (a pseudo-peroxidase) with that of lactoperoxidase (a true peroxidase) and copper ions (a non-enzymatic catalyst) across a range of temperatures at pH 5, after which the biological catalysts are compared again at pH 7. By analyzing the ΔC_p ^‡ of these catalysts, it was found that myoglobin exhibits a significant catalytic contribution at both pH levels, suggesting a structural/vibrational or some other relatively significant transition during the reaction. The study's findings provide a new perspective into myoglobin's enzymatic role in peroxide decomposition and highlight the utility of MMRT in quantifying the contribution of polypeptide chains in enzyme-catalyzed peroxidase reactions. Additionally, our research notes the pH-dependence of myoglobin's catalytic efficiency compared to traditional peroxidases, offering implications for understanding its broader biological roles.