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PHOTOADDITION OF 8‐METHOXYPSORALEN TO E. coli DNA POLYMERASE I. ROLE OF PSORALEN PHOTO‐ADDUCTS IN THE PHOTOSENSITIZED ALTERATIONS OF POL I ENZYMATIC ACTIVITIES

Abstract— We have previously demonstrated that 8‐methoxypsoralen (8‐MOP)‡ plus UVA is able to inactivate the three enzymatic activities of E. coli DNA polymerase I and that oxygen is required for these reactions (M. Granger et al., (1982) Photochem. Photobiol., 36, 175–180). We now show that UV‐A irradiation produces a covalent incorporation of the psoralen derivative into the enzyme either in the presence or in the absence of oxygen. The excited psoralen binds directly to the protein in an oxygen‐independent reaction; no complex was detected in the absence of irradiation. Fluorescence measurements reveal that at least two photoadducts are formed.