PHOTOBIOLOGICAL ACTIVITY OF 4‐METHYLPSORALEN and 4‐METHYL‐4‘,5’‐DIHYDROPSORALEN WITH RESPECT TO LETHAL and MUTAGENIC EFFECTS ON E. coli, and PROPHAGE INDUCTION

Abstract

Abstract— The lethal and mutagenic effects on E. coli as well as the induction of prophage lambda were determined after treatment with 4‐methylpsoralen, 8‐methoxypsoralen, psoralen or 4‐methyl‐4′,5′‐dihydropsoralen and UV‐A irradiation. All psoralens used caused photokilling and photomutagenesis of strains H/r30R and Hs30R. 4‐Methylpsoralen was more efficient for killing and for the induced mutation than 8‐methoxypsoralen or psoralen in view of the dose modification factor. This finding can be explained by the methylation effect of psoralen. 4‐Methylpsoralen induced more mutation in Hs30R than in H/r30R. Monofunctional 4‐methyl‐4′,5′‐dihydropsoralen required much higher fluence than bifunctional psoralens to kill cells and to induce the mutation. When the induced mutation frequency was expressed as a function of survival, mutagenic efficiency ranked in the following order: 8‐methoxypsoralen > psoralen > 4‐methylpsoralen > 4‐methyl‐4′,5′‐dihydropsoralen. 4‐Methylpsoralen was 3–4‐fold less mutagenic than 8‐methoxypsoralen in this plot. Lytic growth of prophage in E. coli AB1157 (ñ) was induced by the treatment. When the bifunctional psoralens were used, the maximum induced fraction was larger than 20%. However, it was only 2% when 4‐methyl‐4′,5′‐dihydropsoralen was used.