Abstract：
:Escherichia coli DNA photolyase contains a stable flavin radical that is readily photoreduced in the presence of added electron donors. Picosecond, nanosecond, and conventional flash photolysis technique have been employed to investigate the events leading to photoreduction from 40 ps to tens of milliseconds following flash excitation. Direct light absorption by the flavin radical produces the first excited doublet state which undergoes rapid (within 100 ps) intersystem crossing to yield the lowest excited quartet (n pi*) state. In contrast, light absorption by the folate chromophore produces a new intermediate state via interaction of the folate excited singlet state with the ground-state flavin radical, leading to an enhanced yield of the excited radical doublet state and hence quartet state. Subsequent reaction of the excited quartet state involves hydrogen atom abstraction from a tryptophan residue. Secondary electron transfer from added electron donors occurs to the oxidized tryptophan radical with rate constants ranging from 10(4) (dithiothreitol) to 4 x 10(6) M-1 s-1 (n-propyl gallate). The low value of the latter rate compared to reduction of the tryptophan radical in lysozyme suggests that the reactive tryptophan is highly buried in photolyase. A redox potential diagram has been constructed for the ground and excited states involved. It is concluded that the one-electron reduction potential of the excited quartet state of the flavin radical must be at least 1.23 V more positive than the ground state, in agreement with the value of delta E greater than 1.77 V calculated from spectroscopic data.
journal_name
Biochemistryjournal_title
Biochemistryauthors
Heelis PF,Okamura T,Sancar Adoi
10.1021/bi00476a008subject
Has Abstractpub_date
1990-06-19 00:00:00pages
5694-8issue
24eissn
0006-2960issn
1520-4995journal_volume
29pub_type
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