Comparative investigations of the effects of X- and UV-irradiation on lysozyme in the absence or presence of additives

Complete text of publication follows. The radiation damage (X-ray, UV light) of many proteins and other biomolecules has been investigated by various physicochemical techniques. They revealed numerous changes of the local and global structure of the proteins studied, together with alterations of their functional ability. For the comparison of radiation-induced effects, lysozyme was chosen in a case study, because this enzyme is well characterized, both from the radiobiological and physicochemical point of view. Since the 3D structure and many other details of this protein are known, it may also be used for modeling approaches, including visualization of the individual constituents (amino acid residues, surrounding water molecules). Despite many problems and ambiguities concerning an exact comparison of the impact of ionizing and nonionizing radiation, the resultant radiation effects may be correlated quantitatively. A critical analysis of the radiation damages obtained allows determination of 'isoeffective' doses. The doses, which have been derived from activity measurements (e.g., 1 kGy and 30 kJ/m2 in the case of lysozyme), may also be applied successfully for comparing the structural changes occurring after preceding irradiation. A comparison of the radiation effects monitored in the absence of additives reveals that the damages observed after X- and UV-irradiation (inactivation, aggregation, fragmentation, destruction of aromatics and SS bonds, formation of crosslinks and new chromophores, partial unfolding etc.) are similar but differ with respect to the type of irradiation and the conditions applied. Addition of many compounds discloses a quite different behavior of the compounds tested as protectives against X- or UV-irradiation. Some substances may provide a chemical repair of already damaged particles, restoring some of the original molecular features