title: EPR Study of UV-Irradiated Thymidine Microcrystals Supports Radical Intermediates in Spore Photoproduct Formation.
abstract: Spore photoproduct is a thymidine dimer formed when bacterial endospore DNA is exposed to ultraviolet (UV) radiation. The mechanism of formation of this thymidine dimer has been proposed to proceed through a radical-pair intermediate. The intermediate forms when a methyl-group hydrogen atom of one thymidine nucleobase is transferred to the C6 position of an adjacent thymidine nucleobase, forming two species, the TCH2and TH radicals, respectively. Using a series of thymidine isotopologues and electron paramagnetic resonance (EPR) spectroscopy, we show that microcrystals of thymidine exposed to UV radiation produce these two radical species. We observe three sources that donate the additional hydrogen at the C6 position of the TH radical. One of the three sources is the methyl group of another thymidine molecule in a significant fraction of the TH species. This lends support to the radical-pair intermediate proposed in the formation of spore photoproduct.
authors.affiliation: Department of Chemistry, Box 351700, University of Washington , Seattle, Washington 98195, United States.
authors.forename: Ellen C
authors.initials: EC
authors.lastname: Hayes
authors.affiliation: Department of Chemistry and Chemical Biology, 402 N. Blackford Street, LD 326, Indiana University-Purdue University Indianapolis , Indianapolis, Indiana 46202, United States.
authors.forename: Yajun
authors.initials: Y
authors.lastname: Jian
authors.affiliation: Department of Chemistry and Chemical Biology, 402 N. Blackford Street, LD 326, Indiana University-Purdue University Indianapolis , Indianapolis, Indiana 46202, United States.
authors.forename: Lei
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Chemistry, Box 351700, University of Washington , Seattle, Washington 98195, United States.
authors.forename: Stefan
authors.initials: S
authors.lastname: Stoll