Excitation and Fluorescence Spectra of the Chromophore Associated With the Dna‐photoreactivating Enzyme From the Blue–green Alga Anacystis Nidulans

DNA‐PHOTOREACTIVATING enzymes can be classified as deoxyribonucleate cyclobutane dipyrimidine photolyases*. Such an enzyme was recently purified 3760‐fold from the blue‐green alga Anacystis niduluns [8]. The absorption spectrum of the enzyme revealed a small peak at 418 nm that was attributed to an impurity. The enzyme has now been purified further, by affinity chromatography on far‐ultraviolet (far‐u.v.) irradiated DNA non‐covalently bonded to cellulose, and its excitation and fluorescence spectra measured. These spectra reveal the presence of a non protein chromophore associated with the algal photolyase. The peak wavelengths in the excitation and absorption spectra in the visible region are almost identical and close to that observed in the in vitro photoreactivation action spectrum [8], observations supporting the view that this chromophore is involved as a cofactor in DNA photo reactivation.