title: Identification of a pterin derivative in Escherichia coli DNA photolyase.
abstract: DNA photolyase from Escherichia coli contains reduced flavin adenine dinucleotide plus a second chromophore, partially characterized in previous studies. Both chromophores function as sensitizers in catalysis. The second chromophore has been identified as a 6-substituted pterin derivative. The compound is oxidized with permanganate to yield 6-carboxypterin or reduced with sodium cyanoborohydride to yield a 5,6,7,8-tetrahydropterin derivative. The second chromophore exhibits spectral properties (lambda max = 360, 255 nm, pH 2) similar to that observed for 7,8-dihydropterin cations. The compound does not exhibit a spectrally detectable pKa around 4 but is converted to a dication (lambda max = 346, 255 nm) in strong acid (pKa approximately 1). Similar ionization behavior is observed with 7,8-dihydropterin derivatives that are alkylated at N(5). The instability of the second chromophore in weakly alkaline solution is due to a fully reversible conversion to a labile bleached form. As compared with other pterin derivatives, the hydrolytic instability is unusual but is very similar to that observed for 5,6-dialkyl-7,8-dihydropterinium salts. It is proposed that the second chromophore is a 7,8-dihydropterin with substituents at positions 5 and 6. The discovery that a pterin derivative functions as a photosensitizer in DNA repair is apparently the first example of a photobiological function for pterins.
mesh_terms: D004255:Deoxyribodipyrimidine Photo-Lyase / Q000032:analysis*; D004926:Escherichia coli / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D008190:Lyases / Q000032:analysis*; D008345:Manganese; D017895:Manganese Compounds; D010084:Oxidation-Reduction; D010087:Oxides; D011622:Pterins / Q000378:metabolism*; D013053:Spectrophotometry
chemical_list: D017895:Manganese Compounds; D010087:Oxides; D011622:Pterins; C048856:permanganic acid; D008345:Manganese; D008190:Lyases; D004255:Deoxyribodipyrimidine Photo-Lyase