| Summary: | Ultraviolet (UV) radiation is a potent DNA-damaging agent
and a known inducer of mutations and skin cancer. The
increasing incidence of skin cancer has emphasised the
importance of understanding the mechanistic processes
involved in the interaction of UV radiation with DNA.
One of the most significant photoproducts, induced by UV
light, in the DNA molecule is the cis-syn cyclobutane
pyrimidine dimer. These dimers, particularly the cytosinecontaining
dimers, have been implicated in the mutagenic
and carcinogenic effects of sunlight. Dimerisation of
contiguous pyrimidine residues in DNA can result from
direct irradiation (A = 295-310 nm) or photosensitised
irradiation (A > 300 nm) by endogenous photosensitisers.
Direct irradiation of DNA produces a wide range of
photoproducts, whereas triplet photosensitisation of DNA by
acetone produces only thymine, cytosine and cytosinethymine
dimers. Thus, acetone photosensitisation of DNA can
be used in the elucidation of the mechanistic processes
involved in the formation of photoproducts from the direct
irradiation of DNA.
Calf thymus DNA was irradiated in the presence of acetone
at wavelengths greater than 300 nm, using a high pressure
mercury lamp. Experimental conditions investigated were
irradiation time, acetone concentration and DNA
concentration. Irradiated DNA samples were degraded by hot
acid hydrolysis to excise the dimers. The yields of thymine
and cytosine-thymine dimers were able to be quantitated by
reverse phase high performance liquid chromatography with
DV detection.Independent kinetic mechanisms were proposed for thymine
and cytosine-thymine dimerisation in calf thymus DNA. Rate
constants were assigned from experimentally determined
values, values cited in literature and values calculated
from Stern-Volmer steady state analysis of the proposed
mechanisms. Verification of the proposed kinetic mechanisms
was achieved by the comparison of experimental dimer yields
with those calculated from the computer simulation of the
proposed kinetic mechanism. The computer program CAKE
(Computer Analysis of Kinetic Equations) was used to obtain
the simulated data. Good agreement between the experimental
and simulated data was taken as corroboration of the
proposed kinetic mechanism. A section of this work was concerned with the application
of spectroradiometry to determine the amount of light
intensity absorbed by irradiated solutions. The
modification, calibration and operation of a Macam SR 9010
spectroradiometer to achieve this aim is discussed. === Thesis (M.Sc.)-University of Natal, Durban, 1992.
|
|---|
