Protonated forms of poly[d(G-C)] and poly(dG).poly(dC) and Their interaction with berberine

Interaction of Isoquinoline Alkaloids with Polymorphic DNA Structures

“…1) thereof is depicted in the Inset of , an exclusion parameter of 11.8 base pairs, and a cooperativity factor of 22 for berberine -H L -form complexation (Table). It has been reported earlier that, in aqueous buffer, the weak fluorescence of berberine has no pH dependence [27] [28]. The binding of berberine to the H L form enhanced the fluorescence of the alkaloid several fold (Fig.…”

“…3, c). The fluorescence spectra of the berberine -B-DNA complexation showed enhancement in the fluorescence intensity at 530 nm revealing a binding with the B form [27]. From the spectrofluorimetric titration, berberine showed a non-cooperative…”

“…The absorbance of the Z-DNA UV spectrum (curve 2) showed decrease in the absorbance at 295-nm region compared to the B form. The H L form of poly[d(G-C)] at pH 3.4 has a Hoogsteen base-paired structure [27], and is distinctly different from the right-handed B-DNA and left-handed Z-DNA structures [26] [36]. Fig.…”

“…Berberine and palmatine have wide ranging biochemical and pharmacological effects [42 -47] and were demonstrated to possess antitumor activities in vitro and in vivo [48 -50]. Their various biological and pharmacological properties have been discussed in details in several publications [27] [28] [51 -55]. Unlike berberine and palmatine with buckled structure, coralyne (3; Fig.…”

“…Our laboratory has been investigating protonation-induced conformational changes in natural and synthetic DNAs employing diverse spectroscopic tools [25 -28]. From extensive spectroscopic and thermal-denaturation studies, we had advanced that protonation under controlled ionic strengths and temperatures led to the formation of a unique and novel structure in alternating guanine-cytosine polynucleotides designated as H L form [27], while protonated form of homopolymer could not reveal any such structural alteration. This conformation has been characterized to be left-handed with Hoogsteen base pairing.…”