PHOTOCHEMICAL INTERACTION OF FUROCOUMARINS WITH BROMODEOXYURIDINE AND POLYDEOXY‐NUCLEOTIDES CONTAINING BROMODEOXYURIDINE: ITS BIOLOGICAL IMPLICATIONS

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Abstract
Abstract— The photoreaction of 5‐bromodeoxyuridine (BUdR) exposed to 360 nm light in the presence of the furocoumarins, 4,5′,8‐trimethylpsoralen (TMP) and 8‐methoxypsoralen (&MOP), was studied and compared to those of thymidine. BUdR reacted with furocoumarins, producing cyclobutane‐containing adducts, as does thymidine. Furocoumarins reacted also with BUdR‐containing polymer, poly(dA‐BUdR) in the double stranded form, at a rate similar to that of thymidine‐containing polymer, poly(dA‐dT). Polyamines, which slow the photoreactions of TMP with DNA, had no effect on its binding to the two former polynucleotides. It is suggested that because of the similar photoreactions of BUdR and thymidine with furocoumarins, this combination could be used to elucidate the mechanism by which BUdR sensitizes biological systems. In Escherichia coli some sensitization by BUdR of TMP plus 360 nm light killing was observed. It is therefore concluded that at least part of the sensitization of bacteria by BUdR to UV and ionizing radiation is caused by interference with the repair processes. Since no such sensitization was observed in a uvr B mutant, BUdR apparently impairs the efficiency of the excision resynthesis pathway of repair.

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