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D Dasgupta

Publications and source records attributed to D Dasgupta.

At least 19 recordsLinked to original sources
PubMed1995

Role of magnesium ion in mithramycin-DNA interaction: binding of mithramycin-Mg2+ complexes with DNA.

Mithramycin is an anticancer drug that blocks macromolecular synthesis via reversible interaction with the DNA template in the presence of bivalent metal ions such as Mg2+. The role of Mg2+ in this antibiotic-DNA interaction is not clear. We approached the problem in two steps via studies on the interactions between (i) mithramycin and Mg2+ and (ii) mithramycin-Mg2+ complex(es) and DNA. Spectroscopic techniques such as absorption, fluorescence, and CD were employed for the purpose. From equilibrium and kinetic studies, we earlier reported that MTR forms two different types of complexes with Mg2+ [Aich, P., & Dasgupta, D. (1990) Biochem. Biophys. Res. Commun. 173, 689]. The two complexes are referred to as complex I (with 1:1 stoichiometry in terms of mithramycin: Mg2+) and complex II (with 2:1 stoichiometry in terms of mithramycin: Mg2+). In this report, we have further characterized these complexes by fluorescence spectroscopy. Interactions of these complexes with calf thymus DNA were examined to elucidate their binding. Evaluation of binding parameters (intrinsic binding constant and stoichiometry) from spectrophotometric and fluorimetric titrations suggests that the complexes bind differently to the same DNA. Measurement of van't Hoff enthalpies for the interaction of the two ligands and DNA shows that the complex I-DNA interaction is exothermic, in contrast to the endothermic nature of the complex II-DNA interaction. This could originate from a difference in the molecular nature of the interactions between the complexes and calf thymus DNA. Our studies to detect the nature of the groove via which these complexes bind to DNA suggest that both complexes approach via the minor groove of the DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Synthesis of a photoaffinity taxol analogue and its use in labeling tubulin.

A photoaffinity analogue of taxol, N-([3,5-3H]-4-azidobenzoyl)-N-debenzoyltaxol (7), was synthesized and used to photolabel microtubules. Approximately 20% of the noncovalently bound analogue becomes covalently bound upon irradiation at 300 nm. Incorporated label was stable to a 50% ethanol solution and sodium dodecyl sulfate. About 80% of the incorporated label was found in the beta-subunit and 20% in the alpha-subunit. Incorporation did not occur into unpolymerized tubulin, consistent with the fact that taxol binds only to polymerized tubulin, and was decreased by the presence of taxol. Little or no nonspecific labeling occurs. This analogue is currently being used to identify taxol binding site(s) on tubulin.

Affinity Labels↗
PubMed1992

Interaction between antitumor antibiotic chromomycin A3 and Mg2+. I. Evidence for the formation of two types of chromomycin A3-Mg2+ complexes.

Chromomycin A3 (CHRA3) is an antitumor antibiotic which binds to Mg2+. In the present communication, we show, by means of equilibrium spectroscopic studies (such as absorption, fluorescence and circular dichroism), that two types of CHRA3-Mg2+ complexes (of 1:1 and 1.9:1 stoichiometries in terms of CHRA3:Mg2+, respectively) are formed depending on the concentrations of CHRA3 and Mg2+. The rate constant and activation energy for the formation of two complexes are different, thereby reinforcing the proposition that they are different molecular species. This observation is novel and significant in order to understand the anticancer property of the drug. It also provides explanation for earlier observations that site, affinity parameters and mode of interaction of the drug with DNA in the presence of Mg2+ depend on the relative concentration of Mg2+.

Chromomycin A3↗
PubMed1992

Role of magnesium ion in the interaction between chromomycin A3 and DNA: binding of chromomycin A3-Mg2+ complexes with DNA.

Chromomycin A3 is an antitumor antibiotic which blocks macromolecular synthesis via reversible interaction with DNA template only in the presence of divalent metal ions such as Mg2+. The role of Mg2+ in this antibiotic-DNA interaction is not well understood. We approached the problem in two steps via studies on the interaction of (i) chromomycin A3 and Mg2+ and (ii) chromomycin A3-Mg2+ complex(es) and DNA. Spectroscopic techniques such as absorption, fluorescence, and CD were employed for this purpose. The results could be summed up in two parts. Absorption, fluorescence, and CD spectra of the antibiotic change upon addition of Mg2+ due to complex formation between them. Analysis of the quantitative dependence of change in absorbance of chromomycin A3 (at 440 nm) upon input concentration of Mg2+ indicates formation of two types of complexes with different stoichiometries and formation constants. Trends in change of fluorescence and CD spectroscopic features of the antibiotic in the presence of Mg2+ at different concentrations further corroborate this result. The two complexes are referred to as complex I (with 1:1 stoichiometry in terms of chromomycin A3:Mg2+) and complex II (with 2:1 stoichiometry in terms of chromomycin A3:Mg2+), respectively, in future discussions. The interactions of these complexes with calf thymus DNA were examined to check whether they bind differently to the same DNA. Evaluation of binding parameters, intrinsic binding constants, and binding stoichiometry, by means of spectrophotometric and fluorescence titrations, shows that they are different. Distinctive spectroscopic features of complexes I and II, when they are bound to DNA, also support that they bind differently to the above DNA. Measurement of thermodynamic parameters characterizing their interactions with calf thymus DNA shows that complex I-DNA interaction is exothermic, in contrast to complex II-DNA interaction, which is endothermic. This feature implies a difference in the molecular nature of the interactions between the complexes and calf thymus DNA. These observations are novel and significant to understand the antitumor property of the antibiotic. They are also discussed to provide explanations for the earlier reports that in some cases appeared to be contradictory.

Animals↗
PubMed1990

Role of Mg++ in the mithramycin-DNA interaction: evidence for two types of mithramycin-Mg++ complex.

Mithramycin(MTR, structure shown in Figure 1) [and the related compound Chromomycin A3(CHRA3)] are antitumor antibiotics which inhibit DNA dependent RNA polymerase activity via reversible interaction with DNA only in the presence of divalent metal ion such as Mg++. In order to understand the role of Mg++ in MTR-DNA interaction, absorbance and CD spectroscopic techniques are employed to study the binding of MTR to Mg++. These studies show: i) the drug alone binds to Mg++ and ii) two different types of drug-Mg++ complexes are formed at low(Complex I) and high(Complex II) ratios of the concentration of Mg++ and MTR. We propose that these two complexes would bind to the same DNA with different affinities and rates. This result suggests that the relative concentration of Mg++ is an important factor to be taken into account to understand the molecular basis of MTR-DNA interaction.

Circular Dichroism↗
PubMed1990

Comparative clinical evaluation of chandonium iodide and pancuronium bromide as muscle relaxant.

Chandonium iodide, a synthetic non-depolarising neuromuscular blocking agent and pancuronium bromide were clinically compared as muscle relaxants in 62 patients undergoing elective surgery. Anaesthesia was induced by thiopentone sodium and maintained by oxygen and nitrous oxide. Assessment of efficacy of both the muscle relaxants was graded taking into consideration intubating condition and muscular relaxation during surgery. Tolerability was assessed by noting the changes in heart rate, blood pressure and biochemical estimations. Efficacy of chandonium iodide in the dose of 0.15 to 0.18 mg/kg was comparable to that of 0.08 to 0.1 mg/kg of pancuronium bromide. Both the drugs were well tolerated.

Androstenes↗
PubMed1988

Interaction of synthetic analogues of distamycin and netropsin with nucleic acids. Does curvature of ligand play a role in distamycin-DNA interactions?

Distamycin and netropsin, a class of minor groove binding nonintercalating agents, are characterized by their B-DNA and A-T base-specific interactions. To understand the conformational and chemical basis of the above specificities, the DNA-binding characteristics of a novel synthetic analogue of distamycin have been studied. The analogue, mPD derivative, has the requisite charged end groups and a number of potential hydrogen-bonding loci equal to those of distamycin. The difference in the backbone curvatures of the ligands, distamycin, the mPD derivative, and NSC 101327 (another structurally analogous compound), is a major difference between these ligands. UV and CD spectroscopic studies reported here show the following salient features: The mPD derivative recognizes only B-DNA, to which it binds via the minor groove. On the other hand, unlike distamycin, it binds with comparable affinities to A-T and G-C base pairs in a natural DNA. These DNA-binding properties are compared with those reported earlier for distamycin and NSC 101327 [Zimmer, Ch., & Wahnert, U. (1986) Prog. Biophys. Mol. Biol. 47, 31-112]. The backbone structures of these three ligands were compared to show the progressive decrease in curvatures in the order distamycin, mPD derivative, and NSC 101327. The plausible significance of the backbone curvature vis-à-vis the characteristic B-DNA and AT-specific binding of distamycin is discussed. To our knowledge, this is the first attempt (with a model synthetic analogue) to probe the possible influence of backbone curvature upon the specificity of interactions of the distamycin class of groove-binding ligands with DNA.

Circular Dichroism↗
PubMed1987

Interaction of synthetic analogues of distamycin with poly(dA-dT): role of the conjugated N-methylpyrrole system.

Two synthetic analogues of distamycin (Dst), PPA and PAP, containing a saturated beta-alanine moiety substituting for an N-methylpyrrole chromophore were studied for their interactions with the double-stranded alternating copolymer poly(dA-dT).poly(dA-dt) [abbreviated as poly(dA-dT)], with UV absorption and circular dichroism (CD) spectroscopy. The distinctive feature of these analogues is the difference in the extents of extended conjugation due to contiguous pyrrole rings: it decreases in the order Dst greater than PPA greater than PAP. Both these analogues bind to poly(dA-dT) in a way similar to Dst, as suggested from the observed red shift in the UV spectra of the ligands upon complexation and the appearance of induced Cotton effects (in the 290-350-nm region) in the CD spectra of the complexes. A comparative study of (i) the spectral features of the complexes between these ligands, Dst and netrospin (Nt) and poly(dA-dT), and (ii) the binding parameters for the association with the polynucleotide suggests that the number and relative positions of the pyrrole moieties influence the spectral features and thermodynamic stabilities of the complexes, and the latter show a progressive decrease in the order Dst greater than Nt greater than PPA greater than PAP. Implications of these results vis-à-vis the molecular basis of Dst-DNA interaction are discussed.

Circular Dichroism↗
PubMed1987

Enzyme-catalysed non-oxidative decarboxylation of aromatic acids: I. Purification and spectroscopic properties of 2,3 dihydroxybenzoic acid decarboxylase from Aspergillus niger.

In order to understand the molecular mechanism of non-oxidative decarboxylation of aromatic acids observed in microbial systems, 2,3 dihydroxybenzoic acid (DHBA) decarboxylase from Aspergillus niger was purified to homogeneity by affinity chromatography. The enzyme (Mr 120 kDa) had four identical subunits (28 kDa each) and was specific for DHBA. It had a pH optimum of 5.2 and Km was 0.34 mM. The decarboxylation did not require any cofactors, nor did the enzyme had any pyruvoyl group at the active site. The carboxyl group and hydroxyl group in the ortho-position were required for activity. The preliminary spectroscopic properties of the enzyme are also reported.

Aspergillus niger↗
PubMed1987

Interaction of synthetic analogs of distamycin with DNA. Role of the conjugated N-methylpyrrole system in specificity of binding.

Interaction of two synthetic analogs of distamycin (Dst), PPA and PAP, containing a saturated beta-alanine moiety replacing one N-methylpyrrole ring, with different polynucleotides and natural DNAs were studied using UV and CD spectroscopy. The results indicate that, similar to Dst, these analogs bind to DNA via the minor groove with a specificity towards AT-base pairs. It may be proposed that pyrrole chromophores in Dst probably do not play a role in the AT-base selectivity exhibited by Dst.

Base Composition↗
PubMed1986

DNA-binding characteristics of a synthetic analogue of distamycin.

The interaction between a synthetic analogue (structure shown in fig. 1) of distamycin, and DNA has been studied with a view to understanding the conformational and chemical basis of the sequence specific binding of distamycin with DNA. The complex formation between the trimer and DNA is apparent from the red shift in the UV spectrum and appearance of the induced CD band in 300nm-350nm region. The relevant data suggest: (i) the binding is A-T base specific though the specificity is not as pronounced as in distamycin (1,2) and (ii) it occurs via the minor groove of DNA. The partial loss in A-T base specificity may be due to the replacement of N-methyl pyrrole by benzene or the increase in curvature of the backbone of the ligand as a result of this replacement.

Binding Sites↗
PubMed1986

Mode of reversible binding of neocarzinostatin chromophore to DNA: base sequence dependency of binding.

The reversible binding of neocarzinostatin chromophore to polynucleotides was studied in order to understand the molecular basis of its base sequence-specificity in DNA damage production. Studies of the spectroscopic and thermodynamic properties of chromophore-polynucleotide interactions reveal that the binding of the chromophore to poly(dA-dT) is qualitatively and quantitatively different from that to poly(dG-dC) (and poly(dI-dC]. From these and other experiments using double-stranded mixtures of homopolynucleotides, it is proposed that the observed A T specific intercalation might result from differential recognition of minor variations in the B-DNA type structure by the chromophore.

Antibiotics, Antineoplastic↗
PubMed1985

Cryospectrokinetic evidence for the mode of reversible binding of neocarzinostatin chromophore to poly(deoxyadenylic-thymidylic acid).

The spectra of neocarzinostatin (NCS) chromophore during its reversible association with poly(dA-dT).poly(dA-dT) [poly(dA-dT)] were recorded (at intervals of 17 ms or more) by a cryospectroscopic method. Examination of the spectral changes of a drug during its interaction with DNA has not been previously reported. Such studies indicate binding of chromophore to poly(dA-dT) is a two-step process in which the spectral properties of the intermediate poly(dA-dT). NCS chromophore species closely resemble those of the final equilibrium species. On the basis of cryokinetic studies (at single wavelengths) carried out at low temperature (2 degrees C), the following proposed mechanism of the DNA-drug (PD) interaction was quantitated: (Formula: see text). In analogy with the other reports on the kinetics of drug-DNA interaction, (PD)I and (PD)II could represent externally bound and intercalated complexes, respectively. However, since the spectra of (PD)I and (PD)II are closely similar, it can also be proposed that (PD)I and (PD)II represent two forms of an intercalated complex. The rate and equilibrium constant for each step were determined by examining the kinetics of the forward and reverse reactions. This was accomplished by determining the polynucleotide concentration dependence of the apparent fast and slow first-order rate constants observed during a double-exponential increase in transmittance (at 330 nm) associated with the binding and the apoprotein-induced dissociation rate constant of the chromophore from poly(dA-dT). The opportunity to use apoprotein, instead of a detergent, to follow the kinetics of the reverse reaction provides a novel approach to these studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Antibiotics, Antineoplastic↗