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PSORALEN PHOTOLESIONS IN THE PHOSPHOLIPIDS. Zofia Zarebska1, Ewa Waszkowska1, Sergio Caffieri2, Francesco Dall'Acqua2 1Institute of Biochemistry and Biophysics PAS, 02-106 Warszawa, Poland; 2Institute of Pharmaceutical Sciences,Centro del CNR, 35131 Padova, Italy Abstract The formation of d1<>PSO cyclobutane adducts in the model lecithins was shown. The adducts are formed in the both, hydrophylic and hydrophobic media with approximately 5% yield at the pharmacological doses of UVA radiation. The d1<>PSO and d1<>pyrone adducts identified by absorption and NMR spectroscopy can serve as markers of the phospholipid lesions in the cell. It was anticipated that photochemically induced modifications: psoralen photoaddition to the vinyl bonds of fatty acids, fatty acid-adducts release from the lecithin and trans-isomerisation around vinyl bonds - altogether can affect the membrane fluidity and the recognition processes of the membrane receptors [4].