ABSTRACT
Photosynthetic organisms have complex, but elegant, systems for the harvesting and conversion of light energy into useful chemical forms, as long as the wavelength of light is in the visible to near-infrared region. The intensity of ultraviolet (UV) light from the sun and man-made light sources is much higher in the 300-400 nm region than in shorter-wavelength regions. Most of the biological molecules that absorb in the 300-400 nm region are prosthetic groups of proteins, which have primary absorption in the visible and second or third excited state bands in the near UV. Action spectra are defined by the extent of a specific photon-initiated effect as a function of the wavelength of excitation light. Outside of photoisomerization photoionization is the simplest form of photochemistry. Deoxyribonucleic acids (DNA) photolyase is a repair enzyme that reverts UV-induced thymine dimers in DNA by an electron transfer reaction between photoactivated FADH, an electron donor, and the dimer in the DNA-enzyme complex.
