Neutron cryo-crystallography captures the protonation state of ferryl heme in a peroxidase

Abstract

Peroxidase proton placement Heme enzymes catalyze a variety of biochemical oxidations through the activation of oxygen by iron. Casadei et al. used neutron crystallography to elucidate the mechanism of cytochrome c peroxidase (see the perspective by Groves and Boaz). In the highly reactive intermediate state termed compound I, the iron(IV) oxo, or ferryl, fragment was not protonated, whereas a nearby histidine residue was protonated. The sensitivity of neutron scattering to proton locations revealed these protonation states, where more common techniques, such as x-ray diffraction, have yielded more ambiguous results. Science , this issue p. 193 ; see also p. 142