A Comparative Study of Calf Thymus DNA Binding to Cr(III) and Cr(VI) Ions

Abstract

Chromium(VI) salts are well known to be mutagens and carcinogens and to easily cross the cell membranes. Because they are powerful oxidizing agents, Cr(VI) reacts with intracellular materials to reduce to trivalent form, which binds DNA. This study was designed to investigate the interaction of calf thymus DNA with Cr(VI) and Cr(III) in aqueous solution at pH 6.5-7.5, using Cr(VI)/DNA(P) molar ratios (r) of 1:20 to 2:1 and Cr(III)/ DNA(P) molar ratios (r) of 1:80 to 1:2. UV-visible and Fourier transform infrared (FTIR) difference spectroscopic methods were used to determine the metal ionbinding sites, binding constants, and the effect of cation complexation on DNA secondary structure. Spectroscopic results showed no interaction of Cr(VI) with DNA at low anion concentrations (r ‫؍‬ 1:20 to 1:1), whereas some perturbations of DNA bases and backbone phosphate were observed at very high Cr ( Chromium(VI) salts are well known to be mutagens and carcinogens and to easily invade the insides of cells (1). Cr(VI) produced DNA cross-links in rat tissues in vivo (2) and in cultured cells in vitro (3, 4). Although Cr(VI) damaged nuclear DNA in whole cells, no reaction of Cr(VI) with isolated DNA occurred in vitro at physiological pH in the absence of a metabolizing system (5). The Cr(VI) that is taken up is considered to be reduced by glutathione, cysteine, or ascorbic acid into Cr(III) (6), and the resulting cation reacts with DNA to form Cr(III)-DNA adducts. Because Cr(III) is a final form of chromium within the cell, the interaction of Cr(III) with DNA may play crucial role in the carcinogenetic action of Cr(VI) salts.The conversion of B form into Z form in the purine-pyrimidine sequence of DNA has been considered to be a factor in the transcriptional activity of genes (7). Cr(III) is found to interact with the poly(dG-dC) at low concentration and change B form to Z form in the presence of ethanol (8). However, Cr(III) at high concentration causes DNA condensation, inhibiting the alteration of B to Z structure (8). Moreover, the study on the effect of Cr(III) on DNA replication with single-stranded DNA template and micromolar concentration of Cr(III) revealed that Cr(III) bound in a dose-dependent manner to the template DNA and prevents DNA replication (9). However, if the unbound chromium was removed from the system by gel filtration, the rate of DNA replication by polymerase I (Klenow fragment) on the chromium-bound template increased more than 6-fold relative to control. This increase was paralleled by as much as a 4-fold increase in processivity and a 2-fold decrease in replication fidelity. When the concentration of Cr(III) increased further, DNA-DNA cross-links occurred to inhibit the polymerase activity. Trivalent chromium can bind purified DNA and form lesions capable of obstructing DNA replication in vitro (10, 11). It has also been observed that intact Novikoff ascites hepatoma cells exposed to potassium chromate formed cross-linking of nuclear proteins to DNA (12). Recently, Cr(III) was shown to cause mutation...

Structural Analysis of DNA Interactions with Biogenic Polyamines and Cobalt(III)hexamine Studied by Fourier Transform Infrared and Capillary Electrophoresis

“…1B and 2). A similar trend was observed for the DNA band at 1717 cm Ϫ1 , in-plane stretching vibrations of double bond of guanine (C7ϭN) located at the major groove (64,66). This band shifted downward by 4 cm Ϫ1 in the spectra of Spd⅐DNA and Co(III)⅐DNA complexes, whereas in the Put⅐DNA adducts it was displaced by 2 cm Ϫ1 (Figs.…”

“…This decline in the intensity is the consequence of helix stabilization caused by a partial putrescine-phosphate interaction. Such decrease in infrared intensities of DNA vibrations is also observed when cation-phosphate binding resulted in partial helix stabilization (66). In our opinion, putrescine is more fluid than other polyamines at low and high concentrations and seems to bind at different sites, including the binding to the major and minor grooves, as well as the backbone phosphate group stabilizing the DNA duplex at high cation content.…”

“…In this region, the IR spectra of spermine, spermidine, and putrescine show a pair of bands around 1480 and 1319 cm Ϫ1 . In the spectra of Spm⅐DNA and Spd⅐DNA complexes, the former band is overlapped by the band at 1491 cm Ϫ1 involving in-plane ring vibration of cytosine residues (65,66). These two bands are assigned to the polyamine methylene scissoring vibrations (67,68).…”

Utilization of DNA-metal Ion Biomatrix as a Relative Humidity Sensor

“…The biomatrix at 0% RH condition was prepared by the incubation in desiccator with silica gel for 24 h. These spectra were normalization at the 968 cm À1 , related to the deoxyribose C-C stretching vibration, as the internal reference. 13 The IR spectrum was measured with the resolution of 4 cm À1 .…”

Cr3+ Binding to DNA Backbone Phosphate and Bases: Slow Ligand Exchange Rates and Metal Hydrolysis

“…20 The interaction of Cr 3+ with double-stranded DNA results in the DNA inter-strand crosslinking. 21 Because of a strong coordination and slow dissociation kinetics, Cr 3+ can form highly stable Cr 3+ /DNA lesions, 22 inducing its genotoxicity.…”