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PubMed1975

Interaction of 4,5-dibromo-2,7-di-(acetatomercuri)-fluorescein with DNAs of different base composition.

The changes in absorption spectra in the visible region observed on adding different naturally occurring and synthetic DNA duplexes to solutions of 4,5-dibromo-2,7-di-(acetatomercuri)-fluorescein indicate that the mercurial reacts with polynucleotides of this type. The reaction is reversible as proved by adding excess of KCN which restores the original spectra of the free dye. The interaction is characterised also by quenching of the fluorescence of the dye and the induction of optical activity in it. The extent of these spectral effects depends strongly on the (A+T) content of the complexed DNA and decreased in the order: poly [d(A-T)], Clostridium perfringens DAN, Escherichia coli DNA, Micrococcus luteus DNA and poly(dC). From equilibrium-dialysis experiments the same order in affinity is obtained when these poly-nucleotides are at equilibrium with the same concentration of 4,5-dibromo-2,7-di-(acetatomercuri)-fluorescein. From the changes produced by different mercurials in the ORD spectra and viscosity of a DNA solution it has been concluded that 4,5-dibromo-2,7-di(acetatomercuri)-fluorescein does not cause any drastic alteration of the secondary structure of DNA.

Animals↗
PubMed1977

Interaction of palladium (II) with DNA.

The nature of interaction of palladium (II) with calf thymus DNA was studied using viscometry, ultraviolet, visible and infrared spectrophotometry and optical rotatory disperison and circular dichroism measurements. The results indicate that Pd(II) interacts with both the phosphate and bases of DNA. The ORD/CD data indicate that the binding of Pd(II) to DNA brings about considerable conformational changes in DNA.

Animals↗
PubMed1977

Structure of single-stranded virus RNA in situ. II. Optical activity of five tobacco mosaic-like viruses and their components.

ORD and CD spectra of some TM-like viruses and their coat proteins were measured to study a possible role of tryptophan residues in RNA-protein interactions in these viruses. Five viruses of this group, differing in tryptophan content of their coat proteins, were used: v-TM virus (3 tryptophan residues per protein subunit), strains HR and U2 (2 tryptophan residues per subunit), dolihos enation mosaic virus and cucumber virus 4(1 tryptophan residue per subunit). The viruses differ significantly in their ORD and CD spectra and some correlation between these spectra and tryptophan content of coat proteins seems to exist. But an analysis of "intravirus RNA" CD spectra, obtained by subtraction of CD spectra of virus -like protein assemblies from the spectra of intact viruses, shows that the observed differences in optical activity can hardly be explained by tryptophan participation in RNA-protein interactions. The presence of the "additional" peak at 293 nm in the ORD of TM virus had been considered as evidence of tryptophan-RNA interactions in this virus. In the present work such a peak at 293 nm was observed in the ORD of all the 5 viruses studied, irrespective of the tryptophan content in their coat proteins. Besides, we managed to obtain the virus-like protein assemblies preparations which also showed a peak at 293 nm. All these data show that, in all probability, the 293 nm peak in the ORD of TM virus does not result from tryptophan-RNA interactions. It is believed that the difference in the optical activity of RNA particles of TM-like viruses do originate from the differences in the RNA-protein interactions in these viruses, but these interactions can hardly involve tryptophan residues of virus coat proteins.

Circular Dichroism↗
PubMed1979

The enzymatic hydrolysis of the phosphate ester bond in some thionucleotides.

We prepared the 5'- and 3'-O-phosphorothioate esters of the antitumor agent O2 : 2'-anhydro-1-beta-D-arabinosylcytosine. We also included in this study esters of 2'-thio-2'-deoxycytidine, namely, 2'-S-dCyd-2' : 3'-P, 2'-S-dCyd-2'-P, and 2'-S-dCyd-3'-P, along with natural nucleotides. These compounds were subjected to the action of Escherichia coli alkaline phosphatase, potato acid phosphatase, and bovine pancreatic ribonuclease A. The data were analyzed by Lineweaver-Burk plots to obtain Km and KI values. Only 2'-S-dCyd-2'-P was a substrate for alkaline phosphatase; the anhydro-araCyt phosphorothioates were good competitive inhibitors, while 2'-S-dCyd-3'-P did not associate with the enzyme. Acid phosphatase hydrolyzed all four monoesters investigated, including the S-phosphorothioate. The cyclic phosphorothioate, 2'-S-dCyd-2' : 3'-P was neither hydrolyzed by, nor associated with, ribonuclease A. ORD spectroscopy was also used in an attempt to relate the structural features of analogs to the peculiarity of their hydrolysis.

Acid Phosphatase↗