The interaction of native calf thymus DNA with clodinafop-propargyl (CP), in 10 mM HEPES aqueous solutions at neutral pH 7.2, has been investigated by spectrophotometric, circular dichroism (CD), spectrofluorometric, melting temperature (Tm), and viscosimetric techniques. It was found that CP molecules could intercalate between base pairs of DNA as evidenced by hyperchromism in UV absorption band of DNA, an increase in melting temperature, a sharp increase in specific viscosity of DNA, induced CD spectral changes, and increase in the fluorescence of methylene blue (MB)-DNA solutions in the presence of increasing amounts of CP, which indicates that it is able to release the intercalated MB completely. All results suggest that the CP interacts with calf thymus DNA by an intercalative mode of binding.
In this study, we investigated the effects of some denaturants, such as urea and heat, on structure and function of rabbit polyclonal antibody and its Fab fragments. Thermal unfolding studies by circular dichroism of antibody and Fab fragments showed that in acidic pH, antibody has multi-transitions whereas Fab fragments have one transition curve; however in neutral pH, thermal unfolding of both had one transition. Effects of urea on the structure of antibody and Fab were studied through fluorescence spectroscopy. Despite exposure of protein to high concentration of denaturant, partial unfolding occurred in both antibody and Fab, but the denaturation of Fab was more considerable than that of antibody. Functional studies indicated that urea and heat causes a decrease in affinity in both antibody and Fab, but deactivation of Fab is more considerable in comparison with the antibody molecule. Turbidity study of antibody and Fab showed that aggregation of Fab occurred at lower temperatures than that of antibody. Our results indicate that Fab has higher sensitivity in comparison with antibody in the unfolding, deactivation, and aggregation processes. Therefore, our data proposes a stabilizing role for Fc.
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