J. Synchrotron Rad. (2007). 14, 11-23 [ doi:10.1107/S0909049506049806 ]
Abstract: 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.
Keywords: radiolytic reduction; photoreduction; myoglobin; cytochrome P450; chloroperoxidase; microspectrophotometer; energy dependence; hydrated electrons; radical scavengers; radiation damage.
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