Open AccessCryoradiolytic reduction of crystalline heme proteins: analysis by UV‐Vis spectroscopy and X‐ray crystallography
Author(s) -
Beitlich Thorsten,
Kühnel Karin,
SchulzeBriese Clemens,
Shoeman Robert L.,
Schlichting Ilme
Publication year - 2007
Publication title -
journal of synchrotron radiation
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.172
H-Index - 99
ISSN - 1600-5775
DOI - 10.1107/s0909049506049806
Subject(s) - myoglobin , heme , chemistry , hemeprotein , redox , ferric , metalloprotein , photochemistry , ferrous , crystallography , cytochrome , cytochrome c , absorption spectroscopy , x ray crystallography , radiolysis , spectroscopy , molecule , inorganic chemistry , metal , organic chemistry , diffraction , radical , biochemistry , physics , quantum mechanics , mitochondrion , enzyme , optics
The X‐ray crystallographic analysis of redox‐active systems may be complicated by photoreduction. Although radiolytic reduction by the probing X‐ray beam may be exploited to generate otherwise short‐lived reaction intermediates of metalloproteins, it is generally an undesired feature. Here, the X‐ray‐induced reduction of the three heme proteins myoglobin, cytochrome P450cam and chloroperoxidase has been followed by on‐line UV‐Vis absorption spectroscopy. All three systems showed a very rapid reduction of the heme iron. In chloroperoxidase the change of the ionization state from ferric to ferrous heme is associated with a movement of the heme‐coordinating water molecule. The influence of the energy of the incident X‐ray photons and of the presence of scavengers on the apparent reduction rate of ferric myoglobin crystals was analyzed.