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PHOTOCHEMISTRY, PHOTOPHYSICS, AND MECHANISM OF PYRIMIDINE DIMER REPAIR BY DNA PHOTOLYASE
Author(s) -
Kim SangTae,
Sancar Aziz
Publication year - 1993
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1993.tb09232.x
Subject(s) - photolyase , pyrimidine dimer , chromophore , chemistry , photochemistry , flavin group , cofactor , electron transfer , flavin adenine dinucleotide , dimer , dna , dna repair , biochemistry , enzyme , organic chemistry
— DNA photolyases photorepair pyrimidine dimers (PyroPyr) in DNA as well as RNA and thus reverse the harmful effects of UV‐A (320–400 nm) and UV‐B (280–320 nm) radiations. Photolyases from various organisms have been found to contain two noncovalently bound cofactors; one is a fully reduced flavin adenine dinucleotide (FADH ‐ ) and the other, commonly known as second chromophore, is either methenyltetrahydrofolate (MTHF) or 8‐hydroxydeazaflavin (8‐HDF). The second chromophore in photolyase is a light‐harvesting molecule that absorbs mostly in the near‐UV and visible wavelengths (300–500 nm) with its high extinction coefficient. The second chromophore then transfers its excitation energy to the FADH ‐ . Subsequently, the photoexcited FADH ‐ transfers an electron to the Pyr<>Pyr generating a dimer radical anion (Pyr<>Pyr ‐ ) and a neutral flavin radical (FADH ‐ ). The Pyr<>Pyr ‐ is very unstable and undergoes spontaneous splitting followed by a back electron transfer to the FADH ‐ . In addition to the main catalytic cofactor FADH ‐ , a Trp (Trp277 in Escherichia coli ) in apophotolyase, independent of other chromophores, also functions as a sensitizer to repair Pyr <> Pyr by direct electron transfer.