Abstract
CD spectra of (DNA-TOEPyP4) + ZnTOEPyP4, (DNA-ZnTOEPyP4) + TOEPyP4, and DNA + (TOEPyP4-ZnTO- EPyP4) complexes have been studied. It is shown that CD spectra of these triple complexes significantly differ from the DNA-TOEPyP4 and DNA-ZnTOEPyP4 double complex spectra, and they are not sum of these double complexes. Especially some strong differences in CD spectra of the triple and double complexes were observed when both porphyrins were added simultaneously into the DNA solution. In this case, ZnTOEPyP4 revealed a dominant influence on CD spectrum form. Zn-porphyrin also caused a strong intensity of positive band at 416 nm and a negative band at 437 nm when it was added into solution containing the DNA-TOEPyP4 complex. On the basis of obtained data, it was supposed that the observed significant changes in CD spectra of triple complexes were connected to an altered DNA conformation initiated by intercalation of porphyrin TOEPyP4 into GC-rich sites. The melting process analysis of the double complexes was carried out. The mechanisms of individual and joint influence of the porphyrins on DNA, and influence of binding modes on stability of these complexes are also discussed.
Highlights
Among ligands, a special attention is paid to the water soluble cation meso-tetra(4-N-oxyethylpyridil) porphyrins-TMPyP4 type porphyrins-because it is minimal toxic
As it is seen from the figure, addition of porphyrin leads to a significant batochrome shift, which is connected with intercalation of TOEPyP4 into GC rich DNA sites [6,21]
According to data of well studied TMPyP, it was determined that at low mixed ratios of TMPyP4/DNA and moderate ion strength of solutions, the negative CD signal is the main indicator of intercalative binding of porphyrins to GC rich DNA sites, in particular to “5CG3” sites, and the positive CD signal serves as an evidence of outside binding modes [6,9,22]
Summary
A special attention is paid to the water soluble cation meso-tetra(4-N-oxyethylpyridil) porphyrins-TMPyP4 type porphyrins-because it is minimal toxic It predominantly accumulates in tumor cells and binds to G-quadruplex of telomeric DNA [1,2], and defends it from high telomerase activity detaining growth of transformed cells in case of many leukemic diseases [3,4]. The following have been demonstrated: intercalation, outside self-stacking and outside random binding of porphyrins to DNA. It was shown [7] that porphyrin plane molecules TMPyP intercalate between the base pairs of DNA double helix and they bind only to 5’CG3’ areas, and not to other sequences. This is connected to the electrostatic interaction between porphyrin and phosphate groups, but the strong intraplane interaction between porphyrins and DNA have the main contribution in formation of this mode
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