Polymorphic DNA Structures And Their Interaction With Isoquinoline Alkaloids
IR@IICB: CSIR-Indian Institute of Chemical Biology, Kolkata
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| Title |
Polymorphic DNA Structures And Their Interaction With
Isoquinoline Alkaloids
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| Creator |
Bhadra, Kakali
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| Subject |
Chemistry
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| Description |
TITLE: Polymorphic DNA structures and their interaction with isoquinoline alkaloids A. Physicochemical properties of the isoquinoline alkaloids Berberine and palmatine are naturally occurring isoquinoline plant alkaloids exhibiting almost similar absorption and weak fluorescence spectra. On the other hand, coralyne has significantly different absorption and strong fluorescence characteristics. All the three alkaloids are stable in the pH range 2-12. B. Interaction of berberine with polymorphic DNA structures
Spectrophotometric studies- Spectrophotometric analysis revealed AT specific binding with the B-form DNAs showing highest affinity with poly[d(A-T)]. The affinity with others followed the order, poly(dA).poly(dT)> CP DNA>CT DNA >EC DNA> ML DNA > poly[d(G-C)] > poly(dG).poly(dC). Berberine binds to B-form of polypurine-polypyrimidine sequences in synthetic polymers and equally mixed sequences in natural DNAs with positive cooperativity. The cooperativity factor (ω) was maximum with poly(dG).poly(dC) and varied as poly(dA).poly(dT) > CP DNA > EC DNA. With other polymers, berberine showed non-cooperative binding. On the other hand, berberine showed GC specificity and non-cooperative binding with protonated DNAs. The binding
affinity of berberine was higher with the B-form structures compared to HL- and protonated forms. The binding
affinity of berberine-B-DNA complexation decreases with increasing [Na+] ion concentration. The complexation
has more contribution (∼ 65%) from the non-polyelectrolytic forces. Spectrofluorimetric studies- Spectrofluorimetric analysis also revealed AT specificity for the binding of berberine with the B-form DNA and GC specificity for protonated forms, having the same trend in binding affinity as in spectrophotometric data. Enhancement in the fluorescence intensity was comparatively higher with HL and
protonated forms due to the more hydrophobic environment of the complexes. The fluorescence of berberine Bform
DNA complexes was investigated by [Fe(CN)6]4- quenching. The K’SV value was minimum with poly[d(A-T)] complex, indicating that the bound alkaloid molecules are intercalated. Spectropolarimetric studies- Increase in the molar ellipticity was found to be more with the AT polymers and AT rich DNAs for B-DNA complexation, whereas with the protonated forms, the same was maximum with the GC
polymer and GC rich DNAs. No extrinsic CD band was found with the B-form DNAs whereas with the HL and protonated forms, extrinsic CD bands were generated in the 300-400 nm region. The emergence of extrinsic CD bands of opposite signs with the B and HL-form for the bound achiral berberine molecules reflected different binding geometry. This is likely due to the ability of the berberine to differentially bind and discriminate the HL- and B-conformations.
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| Date |
2007
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| Type |
Thesis
PeerReviewed |
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| Format |
application/pdf
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| Identifier |
http://www.eprints.iicb.res.in/38/1/Kakoli_Bhadra_PDF.pdf
Bhadra, Kakali (2007) Polymorphic DNA Structures And Their Interaction With Isoquinoline Alkaloids. PhD thesis, Jadavpur University. |
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| Relation |
http://www.eprints.iicb.res.in/38/
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