Base- and sequence-dependent binding of aristololactam .beta.-D-glucoside to deoxyribonucleic acid

Abstract

The dependence on base-pair composition and sequence specificity of the (aristololactam beta-D-glucoside)-DNA interaction was examined by spectrophotometric, spectrofluorometric, spectropolarimetric, thermal melting, thermodynamic, and viscometric studies. Binding of this alkaloid to various natural and synthetic DNAs was dependent upon the base composition and sequences of DNA. The binding parameters obtained from spectrophotometric analysis, according to an excluded-site model, indicated a relatively high affinity of the alkaloid binding to GC-rich DNA and alternating GC polymer. This affinity was further evidenced by the quenching of fluorescence intensity, decrease in quantum yield, and perturbations in circular dichroic spectrum. The alkaloid stabilized all DNAs against thermal denaturation. The temperature dependence of the binding constants was used to estimate the thermodynamic parameters involved in the complex formation of the alkaloid with various DNAs. The negative enthalpy and entropy change increased with increasing GC content of DNA and also compensated one another to produce a relatively small Gibbs free energy change. Viscometric studies showed that in the strong binding region the increase of contour length of DNA depended strongly on its base composition and sequence of bases, being larger for GC-rich DNA and alternating GC polymer. On the basis of these observations, it is concluded that the alkaloid binds to DNA by a mechanism of intercalation and exhibits considerable specificity toward alternating GC polymer.

Molecular Modes of Action of Defensive Secondary Metabolites

“…The aristolactams I and II (corresponding to the acids I and II) did not form DNA adducts in the presence of S9 (Schmeiser et al, 1988). However, evidence exists that aristolactams can bind to natural and synthetic DNA by a mechanism of intercalation and exhibit considerable specificity towards alternating GC polymers (Nandi et al, 1991). When AA I or II was administered orally to male Wistar rats and the DNA from different target and non-target tissues was analyzed for DNA adducts, the patterns were similar to those obtained from in vitro incubations (Schmeiser et al, 1988).…”

Molecular aspects on the interaction of protoberberine, benzophenanthridine, and aristolochia group of alkaloids with nucleic acid structures and biological perspectives

“…It was established that aristololactam-b-D-glucoside bound to B-DNA by mechanism of intercalation. 170,172 The binding parameters of aristololactam-b-D- 171,172 that the binding of the alkaloid was an exothermic process and the negative enthalpy and negative entropy change increased linearly with increasing GC content of DNA (Fig. 12) and also compensated one another to produce a relatively small Gibbs' free energy change.…”

Molecular aspects on the specific interaction of cytotoxic plant alkaloid palmatine to poly(A)

“…Spectrophotometric titrations were performed by keeping a constant concentration of palmatine and varying the nucleic acid concentration as described earlier [18,42]. Steady state fluorescence measurements were conducted on a Hitachi model F4010 spectrofluorimeter (Hitachi Ltd., Tokyo, Japan) as described earlier [43], where a fixed concentration of the alkaloid was titrated with increasing concentrations of the nucleic acid sample under stirring in fluorescence free quartz cuvettes of 1 cm path length.…”

“…Binding data were analyzed using the software program SCATPLOT [45] version 1.2 that works on an algorithm that determines the best fit parameters to Eq. (5) as described earlier [41,42]. The double stranded poly(A)-palmatine binding result was analyzed according to the Benesi-Hildebrand plot [46] by plotting the variation of C D / Abs against 1/C s yielding a straight line.…”