Evaluation of relative contributions of two enzymes supposed to metabolise hydrogen peroxide in Paracoccus denitrificans

Abstract

A biosensor exploiting an electrochemically mediated enzyme-catalysed reaction was used to quantify relative contributions of cytoplasmic catalase and periplasmic cytochrome c peroxidase to the overall rate of hydrogen peroxide breakdown in cells of Paracoccus denitrificans. The effects of antimycin (an inhibitor of electron flow to cytochrome c peroxidase), the reaction rate versus substrate concentration profiles for the whole cells and subcellular fractions, and the time courses of oxygen concentration demonstrated a profound decrease in the capacity of cytochrome c peroxidase to reduce H2O2 under in vivo conditions. The reason is suggested to be a competition for available electrons between the enzyme and terminal oxidases metabolising oxygen produced by catalase.

MacA, a Diheme c -Type Cytochrome Involved in Fe(III) Reduction by Geobacter sulfurreducens

“…This finding suggests that although MacA has homology to c-type cytochromes that have in vitro peroxidase activity, MacA is not required for G. sulfurreducens to tolerate oxidative stress. This finding is consistent with the suggestion that other c-type cytochromes with homology to MacA that have in vitro peroxidase activity have alternative in vivo functions (14,18,41).…”

Structure and mechanism in the bacterial dihaem cytochrome c peroxidases

“…Although this picture of a role for cytochrome c peroxidase in scavenging hydrogen peroxide generated under hypoxic conditions is self-consistent and plausible, we should note that the experiments of Koutny et al [7] cast doubt on the physiological ability of cytochrome c peroxidase to compete for available electrons with terminal oxidases.…”

Why do bacteria use so many enzymes to scavenge hydrogen peroxide?

“…Inhibitors of the bc1 complex did not slow H 2 O 2 reduction by P. denitrificans , indicating either that this was not the route of electron delivey to CCP or that CCP was not the predominant scavenger under the conditions of the experiment [195]. CCP-encoding genes do not sit adjacent to those of prospective partners.…”