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

A biosensor exploiting an electrochemically mediated enzyme-catalysed react ion was used to quantify relative contributions of cytoplasmic catalase and periplasmic cytochrome c peroxidase to the overall rate of hydrogen peroxi de breakdown in cells of Paracoccus denitrificans. The effects of antimycin (an inhibitor of electron flow to cytochrome c peroxidase), the reaction r ate versus substrate concentration profiles for the whole cells and subcell ular fractions, and the time courses of oxygen concentration demonstrated a profound decrease in the capacity of cytochrome c peroxidase to reduce H2O 2 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. (C) 1999 Elsevier Science B.V. All rights rese rved.