Cryoradiolytic reduction

Cryoreduction of ferric metalloproteins has been mostly done by y-irradiating of frozen solutions of heme proteins at 77K, unless it is specially stated otherwise. Cryoradiolytic reduction of ferric cytochrome c and its complexes with fluoride, azide, cyanide, and imidazole were studied using optical absorption spectroscopy and magnetic circular dichroism.36,39,46 44 The primary products of cryoreduction of low-... 

Using optical absorption spectroscopy, we have studied the dose-dependent yield of cryoradiolytic reduction of the metmyoglobin at a broad protein concentration range 0.01-5 mM.66 The yield reached 50% after 2Mrad, was higher than 90% at 16Mrad total dose, and remarkably was the same within the error for all protein concentrations studied. 

EPR and Mossbauer study of two mutants of the mononuclear iron sulfur protein rubredoxin72 compared the results of chemical and cryoradiolytic reduction and concluded that the latter reduction method produces exclusively one reduced species (serine coordinated iron known from the X-ray structure of the ferric protein) because it leaves the coordination of the ferric precursor unaltered. The identity of another spectral form observed in the chemically reduced C42S mutant in solution could not be unambiguously identified. 

Thus, during the last decade, the method of cryoradiolytic reduction has emerged as a new tool to investigate critical intermediates of redox systems. X-ray-induced radiation chemistry is also increasingly recognized both as a potential source of misinterpretations due to measurement-induced changes of the sample, and as a new, important tool in X-ray crystallography, where the irradiation of protein crystals may be used to deliberately alter the redox state of metals, flavins, disulfides, and other cofactors - The... 

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