Study on the interaction mechanism between DNA and the main active components in Scutellaria baicalensis Georgi

Abstract

Binding of baicalein, wogonin and baicalin to fish sperm DNA was studied by using ethidium bromide dye as a fluorescence probe. To study the binding mechanism, the absorption, fluorescence, melting temperature and viscosity measurement were carried out. The experimental results indicated that the planar of flavonoids intercalated to the DNA helix. When bound to DNA, flavonoids showed hyperchromic and blue shift in the absorption spectra and fluorescence quenching (>50%) in the fluorescence spectra. Furthermore, the intercalative binding was consistent with the red shift in the position of λ max in the fluorescence spectra. It was also found that ionic strength had little or no effect on the binding of flavonoids and DNA. Stern-Volmer plots at 25 and 37 • C showed that the quenching of fluorescence by flavonoids was a combined quenching process. The binding site number n, apparent binding constant K A at 25 and 37 • C, and the corresponding thermodynamic parameters G, H, S at 25 • C were obtained. The interaction of flavonoid-metal complexes with DNA was also studied by spectral methods, and the results suggested that the complexes intercalated into DNA.

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“…The thermodynamic parameters show the binding mode [24]. If the binding enthalpy change (∆H) is invariant over a small temperature range [25] the standard molar binding enthalpy (∆H m Ө ), is estimated from the relationship:…”

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“…If the static binding reaction between the DNA and drug happens, and if there are the similar and independent binding sites n in the DNA, namely, if the binding capability of DNA at each binding site is equal, then the composition of the binary complex can be deduced from the following formula: [29][30][31][32] …”

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“…However, a partial and=or nonclassical intercalation of ligand may bend (or kink) the DNA helix, resulting in the decrease of the effective length and the viscosity. [21][22][23] The changes in relative viscosity of DNA are shown in Fig. 8.…”