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BASE RELEASE FROM DNA AND POLYNUCLEOTIDES UPON 193 nm LASER EXCITATION
Author(s) -
Gurzadyan Gagik G.,
Gorner Helmut
Publication year - 1992
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.1751-1097.1992.tb02173.x
Subject(s) - polynucleotide , guanine , chemistry , thymine , cytosine , dna , adduct , aqueous solution , glycosidic bond , guanosine , radical , base pair , stereochemistry , photochemistry , nucleotide , biochemistry , organic chemistry , gene , enzyme
Abstract— Release of bases from calf thymus DNA and three polynucleotides, induced by 20 ns excitation at 193 nm in aqueous solution at pH 7, was detected by HPLC. The quantum yields of formation of free bases (Φ B ) from double‐stranded DNA (0.4 mM) are independent of intensity, indicating a one‐quantum mechanism of N ‐glycosidic bond cleavage. The Φ B values increase in the order guanine, thymine, adenine, cytosine, the latter being Φ C = 7 × 10 − ‐ 4 for double‐stranded DNA under Ar and O 2 . The larger at l values in N 2 O‐saturated solution, e.g . Φ c = 1.2 × 10 − ‐ 3 are ascribed to additional base release via OH‐adduct radicals. The Φ B values of homopolynucleotides increase in the order poly(G), poly(A) and poly(C), e.g . Φ c‐ = 7 × 10 − ‐ 2 under Ar, as do the efficiencies for base release per radical cation (n B ). A comparison of the n B values with the efficiencies of single‐strand breakage for poly(C), poly(A) and DNA shows a similar trend; both are markedly larger for pyrimidines than for purines. Pathways to undamaged bases, initiated from base radical cations, are proposed.