How does an enzyme detoxify the cells of living beings?

Cytochrome c peroxidase (CcP) is an enzyme thought to detoxify the cells of numerous living beings by reducing hydrogen peroxide (H2O2) to water. This process results in a meta-stable state of CcP historically called compound I. Just like in the haemoglobin that carries oxygen in our blood system, the reduction of H2O2 occurs because CcP has an iron-containing centre that bonds with oxygen. However scientists do not seem to agree on the nature of the bond between the CcP iron atom and the oxygen, which has been cause of dispute for the past 30 years.

Molecular structure of CcP

CcPenzyme with a detail from the active center. © Andreas Ostermann / TUM

One of the main questions to unveil is whether the iron-bonded oxygen atom carries a hydrogen atom or not. Given that neutron scattering is a particularly suitable technique to determine the position of hydrogen atoms, to shed new light on the issue a group of scientists conducted neutron experiments to investigate the CcP enzyme crystals. To guarantee that during the analysis the enzyme was in the compound I state the experiments were conducted at temperatures as low as -173°C.

Surprisingly the results show that oxygen does not bond to hydrogen but only to the CcP ferrous centre. Another surprising finding was that a residue in the CcP active centre carries two hydrogen atoms rather than only one as expected. This means that the whole process of reduction of H2O2 to water by CcP needs to be reassessed.

Original publication: DOI: 10.1126/science.1254398

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