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Biomedical subjects

M Maiti

Publications and source records attributed to M Maiti.

At least 37 records · Page 2Linked to original sources
PubMed1990

Interactions of berberine with poly(A) and tRNA.

The interaction of berberine chloride with poly(A) and tRNA has been studied by various spectroscopic techniques. Binding parameters determined from spectrophotometric and spectrofluorimetric measurements by Scatchard analysis indicate a very high effective binding capacity of berberine to poly(A) as compared to DNA or tRNA. The circular dichroism studies show that binding of berberine to poly(A) causes a significant change in the circular dichroic spectrum of poly(A) itself, as manifested by (i) a decrease of both positive and negative bands and (ii) appearance of a conservative type of extrinsic circular dichroic spectrum in the wavelength range of 300-400 nm, while it does not cause any significant alteration to the A form structure of tRNA. It is concluded that berberine interacts stronger with poly(A) than DNA or tRNA. The results are interpreted in terms of its reported biological activities.

Berberine↗
PubMed1990

Thermodynamics of the interaction of aristololactam-beta-D-glucoside with DNA. Ionic strength dependence of enthalpy and entropy.

The interaction of aristololactam-beta-D-glucoside with calf thymus DNA has been studied by measuring the changes in the absorbance of the alkaloid over a wide range of temperatures and sodium chloride concentrations. The binding parameters obtained are best fit by the neighbour exclusion model. The salt and temperature dependence of the binding constants are used to estimate the thermodynamic parameters involved in the interaction of the alkaloid with DNA. It is observed that aristololactam-beta-D-glucoside binding to DNA is an exothermic process over the entire range of salt and temperature, and the estimated values of enthalpy and entropy change are strongly dependent on the ionic strength of the solution. The enthalpy and entropy changes compensate one another to produce a relatively small Gibbs' free energy change. The possibility that aristololactam-beta-D-glucoside exists as a monovalent cation at neutral pH and the possible molecular contribution to the enthalpy and entropy changes of the aristololactam-beta-D-glucoside-DNA complex are discussed.

Alkaloids↗
PubMed1989

Aristololactam-beta-D-glucoside. A new DNA binding monofunctional intercalating alkaloid.

The binding of aristololactam-beta-D-glucoside to DNA is characterized by hypochromism and bathochromism in the absorption band, quenching of the fluorescence intensity, increase in the positive and negative ellipticity of DNA, enhancement of thermal transition temperature, sign and magnitude of thermodynamic parameters, increase of the contour length of sonicated rod-like DNA and induction of the unwinding-rewinding process of covalently closed superhelical DNA. Binding parameters determined from absorbance and fluorescence titration by Scatchard analysis, according to an excluded-site model, indicate a very high affinity towards DNA. The binding of the alkaloid is an exothermic process with Gibbs free energy of -7.4 kcal/mol, van't Hoff enthalpy of -13.8 kcal/mol and entropy of -21.5 cal/degree/mol at 25 degrees. On the basis of these observations it is concluded that aristololactam-beta-D-glucoside binds to DNA by a mechanism of intercalation.

Alkaloids↗
PubMed1989

Furazolidone-induced interstrand cross-links in Vibrio cholerae DNA. Study of conformational change by circular dichroism.

Vibrio cholerae DNA bearing furazolidone-induced interstand cross-links show a change in the characteristic circular dichroism spectra of the DNA itself in dilute buffer. The change in c.d. spectra was characterized by a shift of the positive band around 272 nm to lower wavelength and a loss of ellipticity of the negative band around 242 nm, and is similar to that exhibited by mitomycin linked Vibrio cholerae DNA under identical conditions and is suggestive of a conformational change of DNA bearing such cross-links. Both furazolidone-induced and mitomycin-induced cross-linking of Vibrio cholerae DNA inhibited the salt-induced conformation change, i.e. increase in winding angle of DNA, the percentage inhibition being greater for mitomycin-linked DNA.

Buffers↗
PubMed1989

Interaction of berberine chloride with deoxyribonucleic acids: evidence for base and sequence specificity.

The interaction of berberine chloride with natural and synthetic DNAs of differing base composition and sequences was followed by various spectroscopic and viscometric studies. The binding of berberine chloride was characterized by hypochromism and bathochromism in the absorption bands, enhancement of fluorescence intensity, stabilization against thermal denaturation, perturbations in the circular dichroic spectrum, increase in the contour length of sonicated rod-like DNA and induction of unwinding-rewinding process of covalently closed superhelical DNA, depending on the base composition and sequences of base pairs. Binding parameters determined from absorbance and fluorescence titration by Scatchard analysis, according to an excluded-site model, indicated a very high specificity of berberine to AT-rich DNAs and alternate AT polymer. Fluorescence quantum yield was maximum for the complexes with AT-rich DNAs and alternate AT polymer. Taken together, these results suggest that berberine chloride exhibits considerable specificity towards alternating AT polymer and binds to AT-rich DNAs by a mechanism of classical intercalation.

Berberine↗
PubMed1988

Heat-induced changes in the conformation of alpha- and beta-crystallins: unique thermal stability of alpha-crystallin.

Of the crystallin proteins of the lens, the principal subunit of the beta-crystallin, beta B2 (beta Bp), has been considered to be the only heat-stable protein because it does not precipitate upon heating. In our recent investigations, however, we have found that the alpha-crystallin from bovine lenses is not only heat stable but also does not denature at temperatures up to 100 degrees C. Using circular dichroism and fluorescence to monitor the conformational changes of alpha- and beta B2-crystallins upon heating, we found that alpha-crystallin maintains a high degree of structure, whereas the beta B2-crystallin shows a reversible sigmoidal order-disorder transition at about 58 degrees C.

Animals↗
PubMed1987

Spectropolarimetric determination of the guanine-cytosine content of DNA.

A circular dichroism technique for the determination of DNA base composition in terms of the guanine-cytosine content has been developed. A linear relationship between the ratio of ellipticities at 260 and 280 nm (theta 260/theta 280) and base composition of DNA is obtained in citrate-phosphate buffer, pH 3.0 at 20 degrees C. The DNA base composition obtained with this method is not only highly reproducible but is also the fastest method reported.

Base Composition↗
PubMed1987

Circular dichroism of sanguinarine-DNA complexes: effect of base composition, pH and ionic strength.

The interaction of sanguinarine with various naturally occurring and synthetic deoxyribonucleic acids of different base composition and sequence has been studied from the measurement of circular dichroism spectroscopy in buffer of various ionic strengths and pH values where physico-chemical properties of DNA remain unchanged. Binding of sanguinarine to DNA causes a change in the circular dichroism spectrum of DNA itself by showing the increase of both positive and negative bands and appearance of a broad positive band with peak at 340 nm. All systems studied exhibit extrinsic positive band that is independent of DNA base composition and sequence. Calf thymus DNA-sanguinarine complexes in different salt concentrations show that, at saturation, the magnitude of molar ellipticity at 340 nm increases with decreasing sodium ions concentration. Sanguinarine-DNA complexes in buffer of various pH values also show that the molar ellipticity at 340 nm is greater in acidic pH and lower in alkaline pH. It is concluded that the alterations of secondary structure of DNA upon binding of sanguinarine is maximum in buffer of low ionic strength and acidic pH and the number of bound alkaloid molecules per base pair, at saturation, is more in G-C rich DNA than in A-T rich DNA.

Alkaloids↗
PubMed1985

Binding of sanguinarine to deoxyribonucleic acids of differing base composition.

The binding of the alkaloid sanguinarine to natural DNAs of differing GC content has been studied by spectrophotometry and viscometry techniques. Binding parameters determined from spectrophotometric measurements by Scatchard analysis, according to an excluded-site model, indicate a very high specificity of sanguinarine binding to GC rich DNA. In the strong binding region, the increase of contour length of DNA depends strongly on its base composition, being larger with GC rich DNA than with AT rich DNA. It is concluded that the alkaloid binds preferentially to the GC pairs in DNA template.

Alkaloids↗