4'-AMINOMETHYL-4,5',8-TRIMETHYLPSORALEN PHOTOCHEMISTRY - THE EFFECT OF CONCENTRATION AND UVA FLUENCE ON PHOTOADDUCT FORMATION IN POLY(DA-DT) AND CALF THYMUS DNA

The photochemistry of 4'-aminomethyl-4,5',8-trimethylpsoralen (AMT) wi th poly(dA-dT) and calf thymus DNA was studied. The extent of photoadd uct formation and the distribution of photoadducts (3,4- and 4',5'-mon oadducts and crosslinks) were determined by liquid scintillation analy sis and HPLC, respectively. The adducts were characterized on the basi s of their UV absorption spectra and mass spectral analysis. The high DNA binding constant for AMT (1.5 x 10(5) M(-1)) led to a high fractio n of intercalated molecules, which contributed to the high level of AM T photoadduct formation, as many as 102 adducts per kilobase pair. In addition, there is a distinct difference in the adduct distribution co mpared to the previously studied 8-methoxypsoralen (8-MOP). Under the conditions employed for the photochemical studies, virtually all of th e AMT molecules in solution are intercalated, occupying 25% of the bas e pair sites. Under similar conditions, 8-MOP molecules occupied 10 ti mes fewer sites. Thus, for AMT, DNA base pair sites other than 5'TA, t he well-characterized strong binding for psoralens in general, are an additional target for photomodification, which results in the formatio n of a higher percentage of monoadducts. The proportion of photoadduct s formed was virtually independent of AMT concentration and UVA (320-4 00 nm radiation) fluence.