Protein-mediated Mn oxidation

Biotic processes of manganese oxidation by bacteria have been studied widely. However, in the current literature, there is no full explanation of how apoferritin mediates the formation of Mn oxides inside its cavity. To elucidate the mechanism by which Mn(III) oxy-hydroxide (MnOOH) nanoparticles form biomineralization in apoferritin, we first identified the phase of solid Mn(III) formation in the cavities of apoferritin to be α-MnOOH, from surface characterizations. Using the colorimetric method, our kinetic analyses of α-MnOOH core formation under varied experimental conditions suggested that Mn²⁺ and OH^- are rate-determining agents, with orders of reaction of 2 and 4, respectively. Based on the kinetics analyses, we proposed that the enzymatically-catalyzed Mn oxidation and hydrolysis occur through sequential steps at the ferroxidase center. This study reveals key kinetics and mechanistic information of the Mn-apoferritin systems, and the results can facilitate applications of apoferritin as a means of nanomaterial synthesis.