Isolation and partial characterization of a novel psoralen-tyrosine photoconjugate from a photoreaction of psoralen with a natural protein.
The photoreaction of psoralens with DNA is a well-characterized reaction. However, the photoreactions of psoralens with proteins is not very well understood. Our objective was to isolate an amino acid-psoralen photochemical adduct. We photoreacted 8-methoxypsoralen (8-MOP) with T7 RNA polymerase, a protein that carries out the fundamental biological process of transcription. Amino acid composition analysis of the photoreacted polymerase revealed that tyrosines quantitatively reacted with 8-MOP. From the acid hydrolysates of the photoconjugated T7 RNA polymerase, an 8-MOP-tyr adduct was partially purified by HPLC. The purified 8-MOP-tyr adduct and related parent compounds were analyzed by UV-visible absorption, fluorescence and mass spectroscopy. Excitation/absorption spectra suggested that the pyrone of the original 8-MOP was modified in the isolated photoadduct, and that the adduct probably contained a benzofuran. Chemical ionization mass spectrometry was consistent with the photoaddition of tyr to 8-MOP with a conservation of the overall mass (+/-1 atomic mass units). As far as we know, this work represents the first instance of isolation and partial characterization of an amino acid-psoralen photoadduct.
Sastry
S S
SS
Laboratory of Molecular Genetics, Rockefeller University, New York, NY 10021, USA. sastrys@rockvax.rockefeller.edu
D017123:Bacteriophage T7 / Q000201:enzymology; D002851:Chromatography, High Pressure Liquid; D012321:DNA-Directed RNA Polymerases / Q000737:chemistry*; D008730:Methoxsalen / Q000737:chemistry* / Q000302:isolation & purification; D010777:Photochemistry; D013057:Spectrum Analysis; D014443:Tyrosine / Q000737:chemistry* / Q000302:isolation & purification; D014764:Viral Proteins
D014764:Viral Proteins; D014443:Tyrosine; C062210:bacteriophage T7 RNA polymerase; D012321:DNA-Directed RNA Polymerases; D008730:Methoxsalen