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|Title:||Identification of Near-Uv Chromophores and Characterization of Cellular Responses to Near-Uv Damage and Oxygen Stress|
|Author(s):||Lloyd, Robert Edward|
|Doctoral Committee Chair(s):||Tuveson, R.|
|Department / Program:||Microbiology|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||The process in which a chromophore(s) absorbs light energy and transfers it to a cell in a toxic manner is known as the photodynamic effect. DNA is the primary chromophore in the UV-C region of electromagnetic spectrum (100-280nm; also known as Far UV or germicidal-UV), and its interaction with UV-C has been extensively studied. However, DNA has very little absorbance in the UV-A region (315-400nm). The identification of chromophores that do absorb in the UV-A and UV-B region (280-315nm) is particularly important due to the potential decrease in protection from the ozone layer.
Riboflavin was shown to act as a UV-A photosensitizer. Two E. coli riboflavin auxotrophs were more resistant to UV-A inactivation when grown with limiting concentrations of riboflavin. Most photosensitizers identified previously were organic. However, Cu(II) in the presence of UV-B radiation, was shown to generate single strand breaks in the sugar-phosphate backbone of pBR322 plasmid DNA. Concomitant with the damage to the DNA backbone was a loss of transforming activity. Reactive oxygen species are often generated by photosensitizers, and air was required for generation of the single strand breaks, but not for the loss of transforming activity. These data suggest a model based on the mechanism of bleomycin generated DNA damage. A DNA glycosylase (formamidopyrimidine glycosylase, Fpg), that participates in the repair of certain DNA nitrogenous base damage, did not repair plasmid DNA damaged by Cu(II).
Cells have developed several systems for repairing or preventing damage from reactive oxygen species. Superoxide dismutase (Sod) protects cells from $\rm H\sb2O\sb2$ and UV-A stress. Several enzymatic systems that affect the topology of a DNA molecule were characterized for their ability to protect cells from oxidative and UV-A stress. Mutants defective in DNA ligase or gyrase were sensitive to these stresses compared to parent strains. The pattern of sensitivity was virtually identical for stress caused by both UV-A and hydrogen peroxide. This gives additional support to the idea that the interaction of UV-A or UV-B with a chromophore generates reactive oxygen radicals.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1992.
|Date Available in IDEALS:||2014-12-17|