Photoreactions of thymine and thymidine with N-acetyltyrosine

Abstract

We report here the photoinduced formation of a thymine-N-acetyltyrosine adduct. Irradiation of dilute solutions of thymine in the presence of N-acetyltyrosine (NAT) leads to the formation of N-acetyl-4-hydroxy-3-(6-hydrothymin-5-yl)phenylalanine (I), isolated as a mixture of the 5R and 5S diastereoisomers; the photoreaction occurs when irradiation is done either at lambda = 254 nm or at wavelengths of lambda > 290 nm. Irradiation of thymidine in the presence of NAT and of thymine in the presence of tyrosine leads to analogous photoadducts. The photoreaction of thymine with NAT is completely quenched by oxygen and cannot be sensitized by acetone. The likely mechanism involves initial photoionization of the amino acid and deprotonation to form the phenoxyl radical. Thymine then probably captures the released aqueous electron, leading to protonation at C6 of the resulting radical anion. Combination of the phenoxyl and 5,6-dihydrothymin-5-yl radicals would then lead to formation of the final products. The quantum yield for production of the thymine-NAT adduct at pH 7.8 was estimated to be about 5.5 x 10(-4), while a value of 2.3 x 10(-3) was estimated for production of corresponding thymidine adduct at pH 8.1. The dependence of the quantum yield for adduct formation on pH has been determined for both the thymine and thymidine reactions with NAT; the maxima in the quantum yield profiles occur at pH 8-8.5, while appreciable values were measured at pH 7.5. We have also demonstrated that a similar reaction occurs when tyrosine is located within a peptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding and Beyond: What Else Can G‐Quadruplex Ligands Do?

“…Indeed, at 12.5 µM concentration of compound 41 , 63.7 % alkylation yield was obtained, significantly higher than previously achieved, with only trace amounts of alkylation observed for non‐G4 single‐stranded or duplex DNA. In addition to mass spectrometry analysis, the group synthesized several mutant analogues of telo22 identify the precise modification sites in combination with digestion assays, demonstrating alkylation preferentially occurs at T12 and T6, in agreement with previous reports that phenoxide radicals preferentially target thymidine nucleobases …”

“…In addition to mass spectrometry analysis, the group synthesized several mutant analogues of telo22 identify the precise modification sites in combination with digestion assays, demonstrating alkylation preferentially occurs at T12 and T6, in agreement with previous reports that phenoxide radicals preferentially target thymidine nucleobases. [146]…”

Analysis of protein–nucleic acid interactions by photochemical cross‐linking and mass spectrometry

“…The ultimate goal of performing photochemical crosslinking and mass spectrometric analysis of protein-oligonucleotide complexes is to answer at the same time which Shaw, Falick, & Shetlar (1992) 10 1 LSIMS Sector MS Shivanna et al (1993) 17 1 FAB Sector MS Jensen et al (1996) 11 6 ESI Triple quadrupole Qin & Chait (1997) 17 1 1 MALDI Quadrupole ion trap 7/7 1/2 LSIMS Sector MS Golden et al (1999) 9 2 ESI Quadrupole ion trap Rieger et al (2000) 7 2 ESI 2 Triple quadrupole Deterding et al (2000) 13 2 ESI Quadrupole TOF Gafken, Mosbaugh, & Barofsky (2000) 11/20/18 2/2/2 ESI Ion trap Steen et al (2001) 12 3 nanoESI Quadrupole TOF This table lists the various studies that describe the sequencing of the peptide moieties from peptide-oligonucleotide heteroconjugates by MS. The lengths of the peptide and the nucleotide moieties, the number of phosphomoieties, the ionization technique, and the type of mass analyzer are shown as well.…”

“…Nevertheless, the first reports about MS/MS-analyses of peptide nucleoside heteroconjugates, written in 1992 (Shaw, Falick, & Shetlar, 1992;Shivanna et al, 1993), used FAB and LSIMS, respectively, in combination with sector tandem mass spectrometers. However, these instruments lacked the sensitivity of current (nano-)ESI or MALDI techniques combined with quadrupole or TOF mass analyzers.…”

“…Even though the first reports of cross-linking of DNA to proteins with UV-light date back to the early 1960s (Alexander & Moroson, 1962;Smith, 1962), the use of MS for the analysis of the generated heteroconjugates started only 30 years later. The first reports on mass spectrometric analysis of peptide-nucleoside/nucleotide heteroconjugates were published in the early 1990s (Shaw, Falick, & Shetlar, 1992;Shivanna et al, 1993). However, at that time only mononucleotides or nucleosides were photochemically cross-linked to peptides, and the phosphate moiety was removed prior to mass spectrometric analysis, which greatly simplifies structural analysis by MS.…”