Abstract
DNA photolyase (PL) is a monomeric flavoprotein that binds cyclobutylpyrimidine dimers (CPDs) and repairs them via photoinduced electron transfer from a reduced flavin adenine dinucleotide cofactor (FADH-) to the CPD. In spite of significant effort, the repair mechanism remains poorly understood. We have used femtosecond transient absorption spectroscopy to explore the electron transfer and repair kinetics of A. nidulans DNA photolyase with oligothymidine substrates in real time. Dimeric substrates show a concentration dependent mixture of kinetics representing bound and unbound substrate. A longer pentameric substrate shows faster electron transfer than previously observed. Repair of the carbon-carbon double bonds (C=C) in the CPD appears to be complete by 1,500 ps. Target analysis of the kinetics is unable to distinguish between sequential and concerted models for the repair reaction, although the data are suggestive of the former.
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