Insights Into How Heme Reduction Potentials Modulate Enzymatic Activities of a Myoglobin‐based Functional Oxidase

Abstract

AbstractHeme‐copper oxidase (HCO) is a class of respiratory enzymes that use a heme‐copper center to catalyze O2 reduction to H2O. While heme reduction potential (E°′) of different HCO types has been found to vary >500 mV, its impact on HCO activity remains poorly understood. Here, we use a set of myoglobin‐based functional HCO models to investigate the mechanism by which heme E°′ modulates oxidase activity. Rapid stopped‐flow kinetic measurements show that increasing heme E°′ by ca. 210 mV results in increases in electron transfer (ET) rates by 30‐fold, rate of O2 binding by 12‐fold, O2 dissociation by 35‐fold, while decreasing O2 affinity by 3‐fold. Theoretical calculations reveal that E°′ modulation has significant implications on electronic charge of both heme iron and O2, resulting in increased O2 dissociation and reduced O2 affinity at high E°′ values. Overall, this work suggests that fine‐tuning E°′ in HCOs and other heme enzymes can modulate their substrate affinity, ET rate and enzymatic activity.