X‐ray Studies on Cytochrome C Peroxidase

An X‐ray crystallographic investigation of the enzyme cytochromecperoxidase is in progress. This report describes experimental methods for the X‐ray diffraction work. The crystals of the enzyme are orthorhombic with cell dimensionsa ‐108.0 Å, b –77.8 Å, and c =51.4 Å. The space group is P212121. Projection data of the native enzyme have been recorded using Ni‐filtered and graphite‐monochromatized Cu K radiation. The ratioI graphite/Iniof about 0.8 was obtained for the diffracted beams. With graphite monochromatized radiation the disintegration of the crystals decreased and the accuracy of the intensity measurements increased due to the improved peak‐to‐background ratios.