INTERACTIONS OF ARISTOLOLACTAM BETA-D-GLUCOSIDE WITH RIGHT-HANDED ANDLEFT-HANDED FORMS OF SYNTHETIC DEOXYRIBONUCLEIC-ACID - SPECTROSCOPIC AND THERMODYNAMIC STUDY

The interaction of aristololactam beta-D-glucoside (ADG) with differen t polymorphic structures of poly(dG-me(5)dC). poly(dG-me(5)dC), poly(d G-dC) . poly(dG-dC), and poly(dI-dC) . poly(dI-dC) has been studied by spectrophotometric, spectrofluorimetric, circular dichroism, UV melti ng profiles, and thermodynamic analysis. The binding of ADG to B-form duplexes is characterized by the typical bathochromic and hypochromic effects in the absorption spectrum, quenching of steady-state fluoresc ence intensity, a decrease in fluorescence quantum yield of ADG, an in crease in fluorescence polarization anisotropy, an increase of thermal transition temperature, and perturbation in circular dichroic spectru m. Scatchard analysis indicates that ADG binds to the right-handed for m of each polymer in a noncooperative manner. Comparative binding para meters determined from absorbance titration by Scatchard analysis, emp loying the excluded site model, indicate a stronger binding of ADG to the B-form of poly(dG-me(5)-dC) . poly(dG-me(5)dC) than to the B-form of poly(dG-dC) poly(dG-dC) or poly(dI-dC) . poly(dI-dC). Thermodynamic parameters (Delta G degrees, Delta H degrees, and Delta S degrees) ob tained by van't Hoff analysis of the data show that the process of bin ding to all B-form duplexes is exothermic and enthalpy driven as chara cterized by a favorable negative enthalpy change (Delta H degrees). Th e binding is opposed by a negative entropy change (Delta S degrees) co ntribution, Conformational changes indicate that the alkaloid converts the left-handed form of poly(dG-dC) . poly(dG-dC), and its methylated analogue and high salt form of poly(dI-dC) . poly(dI-dC) to a bound r ight-handed form, while it inhibits both the rate and extent of the B to Z transition. These studies reveal that ADG binds strongly to B-for m polymers while it does not bind to polymers of Z-form.