PHOTO‐CONJUGATION OF 8–METHOXYPSORALEN WITH PROTEINS

Abstract

Abstract— 8–Methoxypsoralen (8–MOP) is shown to form a covalent conjugate with bovine serum albumin (BSA) by UVA irradiation in the presence of 0 2 . The photoreaction is shown to involve oxidation of 8–MOP itself as a first step, producing an oxidation product which reacts readily with protein. Thus, this photoreaction appears to be completely different from the known 8–MOP photo‐cycloaddition reaction with DNA. Among several proteins studied, human serum albumin, histone type 11 , RNAse A and lysozyme also undergo photoinduced addition by 8–MOP. Chemical modifications of various amino acid residues in BSA revealed tyrosine‐OH as one of the reaction sites. Irradiation (12 h) with UVA at 1.78 J/ d s intensity resulted in approximately 1.5 mot of 8–MOP bound to 1 mol of BSA.