[Effect of ultraviolet and visible light on nucleic acids and proteins]

Three possible photochemical reaction mechanisms have been discussed which might cause changes in biological materials: 1. Photoreactions induced in that constituents of cell substrates absorb UV-light by themselves, i. e. heteroaromatic moieties of nucleic acids and proteins. 2. Photoreactions induced in that constituents not belonging to the natural biological system absorb UV-light, i. e. furocoumarins or cancer producing hydrocarbons. 3. Photoreactions induced in that proper sensitizer molecules absorb UV-light or visible light. The latter type of photoreactions consumes molecular oxygen but does not consume sensitizer molecules (photodynamic action). Examples have been given for the three possibilities concerning photochemistry of nucleic acids and proteins. Damages of biopolymers were discussed with respect to their biological consequences. Photodynamic changes in the blood system might be caused either after addition of sensitizers to blood or by sensitizers which are constituents of blood itself, i. e. porphytines.