PubMed Health⌕ Search

Biomedical subjects

K N Ganesh

Publications and source records attributed to K N Ganesh.

At least 19 recordsLinked to original sources
PubMed2003

Structural changes enhance the activity of Chainia xylanase in low urea concentrations.

Low concentrations of urea (1.2 M) stimulated the activity of endo-xylanase from Chainia by 30%. Subtle structural changes in the monomeric protein were reflected in the secondary and tertiary structure of the enzyme as monitored by fluorescence and circular dichroism. Changes in lambda(max) of emission, the fluorescence intensity and the Stern-Volmer quenching constants for acrylamide, measured in the presence of urea, indicated changes in the microenvironment of the Trp residues, suggesting alterations in tertiary structure. The ellipticity changes at 220 nm and Selcon analysis reflected changes in the content of beta-sheet while both the near- and far-UV CD spectra indicated alterations in the secondary and tertiary structure of the protein in presence of urea. The dissociation constant values (K(d)) show very little change in the affinity of the enzyme for the substrate while the k(cat) values suggest enhanced turnover of the substrate in presence of urea. We suggest that low urea concentrations perturb the conformational state of xylanase leading to an open and a more flexible structure, resulting in enhanced catalytic rates.

Acrylamide↗
PubMed2003

Pyrethroid susceptibility & enzyme activity in two malaria vectors, Anopheles stephensi (Liston) &. A. culicifacies (Giles) from Mysore, India.

BACKGROUND & OBJECTIVES: Anopheles stephensi and A. culicifacies are the two major vectors of malaria in Karnataka. These mosquito populations are continuously being exposed directly or indirectly to different insecticides including the most effective pyrethroids. Therefore, there is a threat of insecticide resistance development. We subjected these vectors to larval bioassay using two popular pyrethroids viz deltamethrin and permethrin. An attempt was also made to correlate the activities of certain detoxifying enzymes such as A- esterase, B-esterase, glutathione-S transferase (GST) and glucose-6-phosphate dehydrogenase (G6PD) with the tolerance levels of the two vectors. METHODS: Larval bioassay was carried out following the standard WHO procedure on field-collected larvae. The LC50 and LC90 values were calculated following Probit analysis. Biochemical estimations were done with a U V spectrophotometer and the isozyme studies employing native polyacrylamide gel electrophoresis (PAGE). RESULTS: The results of the larval bioassay revealed that A. stephensi has more tolerance to deltamethrin than A. culicifacies and vice versa for permethrin. Biochemical estimations revealed significantly (P < 0.05) higher levels of A-esterase and GST activity in A. stephensi whereas A. culicifacies showed significantly higher (P < 0.05) levels of B-esterase and G6PD activity. The total larval protein assayed was found to be more (P < 0.05) in A. stephensi. The isozyme profiles also revealed difference in mobility, intensity and the number of bands. INTERPRETATION & CONCLUSION: As these malaria vectors are exposed to different kinds of insecticides, they develop increased enzyme activities to overcome the insecticide pressure. This has enhanced the tolerance level against the pyrethroids tested. Thus, A. stephensi was found to be tolerant to deltamethrin depicting a higher activity of A-esterase and GST enzymes, whereas the higher activity of B-esterase and G6PD has resulted in the development of tolerance to permethrin in A. culicifacies.

Animals↗
PubMed2002

Role of esterases and monooxygenase in the deltamethrin resistance in Anopheles stephensi Giles (1908), at Mysore.

Field collected An. stephensi larvae were colonized in the laboratory for 15 generations and acclimatized. An isofemale line was raised from this colony and the larvae were subjected to continuous deltamethrin selection pressure. LC50 and LC90 values were calculated at every generation. The values indicated that at the end of seventh generation the larvae have developed 87 fold tolerance in terms of LC50 value compared with the first generation. The reason for this kind of resistance was analyzed on the basis of differential activity of A-esterase, B-esterase, glutathione s-transferase (GST) and glucose 6-phosphate dehydrogenase (G6PD). A significant correlation (P < 0.05) was observed with B-esterase and G6PD activity with the rise in the LC50 and LC90 values. However no significant rise were observed in the other enzymes tested such as A-esterase and GST. The isozyme analysis of the A-esterase and B-esterase using polyacrylamide gel electrophoresis (PAGE) have shown differential profiles.

Animals↗
PubMed2001

Aminoethylprolyl (aep) PNA: mixed purine/pyrimidine oligomers and binding orientation preferences for PNA:DNA duplex formation.

[structure in text] The synthesis of (2S,4S)- and (2R,4S)-aepPNA monomers of adenine, guanine, and cytosine (3-5) and their incorporation at appropriate positions into aegPNA sequence 7 leads to mixed aeg-aep backbone/mixed nucleobase PNAs 8-11. The thermal stabilities of the derived duplexes with DNA are found to be dependent on nucleobase and backbone stereochemistry.

Adenine↗
PubMed2001

Pyrrolidyl polyamines: branched, chiral polyamine analogues that stabilize DNA duplexes and triplexes.

[figure: see text] Pyrrolidyl polyamines (III-VI) are conformationally restricted, chiral analogues of linear spermine elaborated by the addition of aminopropyl chains to yield branched diastereomers. It is demonstrated that in concentrations as low as 0.01 mM, these compounds remarkably stabilize DNA duplexes and triplexes through strong electrostatic interactions. The synthesized compounds are potential dendrons with a chiral pyrrolidine core, and such molecules may have potential as DNA delivery and transfection agents.

DNA↗
PubMed2001

Deltamethrin tolerance & associated cross resistance in Aedes aegypti from Mysore.

BACKGROUND & OBJECTIVES: The indiscriminate use of insecticides in public health and agriculture has led to the development of resistance to these insecticides in the vector mosquitoes. To understand the development of resistance to synthetic pyrethroids, selection studies on Aedes aegypti were done at Mysore. METHODS: Ae. aegypti collected from the field were subjected to selection experiment with deltamethrin for 16 generations in the laboratory. Cross resistance test was conducted against permethrin and fenvalerate. RESULTS: Tolerance level was found to increase by 333.83 folds in terms of its LC50 values. Cross resistance of this deltamethrin selected line was tested against permethrin and fenvalerate. The results show that the selected line has developed cross resistance as much as 5.19 and 5.92 folds respectively against permethrin and fenvalerate. INTERPRETATION & CONCLUSIONS: The findings show a continuous elevation in tolerance in Ae. aegypti with increase in deltamethrin selection pressure, and development of cross resistance to other insecticides of the same class. The natural or developed tolerance has its implications in the control of these mosquitoes.

Aedes↗
PubMed2000

Cyanuryl-PNA monomer: synthesis and crystal structure.

[structure: see text] The chemical synthesis and crystal structure of the peptide nucleic acid (PNA) monomer 11 having cyanuric acid as the nucleobase is reported. The crystal structure of 11 shows molecular tapes arising from continuous intermolecular dimeric hydrogen bonding, with successive tapes held by single hydrogen bonds in the backbone.

Crystallography, X-Ray↗
PubMed2000

Recognition of 5-aminouracil (U(#)) in the central strand of a DNA triplex: orientation selective binding of different third strand bases.

A necessary feature of the natural base triads for triplex formation is the requirement of a purine (A or G) in the central position, since only these provide sets of two hydrogen bond donors/acceptors in the major groove of the double helix. Pyrimidine bases devoid of this feature have incompatible complementarity and lead to triplexes with lower stability. This paper demonstrates that 5-aminouracil (U#) (I), a pyrimidine nucleobase analogue of T in which 5-methyl is replaced by 5-amino group, with hydrogen bonding sites on both sides, is compatible in the central position of triplex triad X*U# x A, where X = A/G/C/T/2-aminopurine (AP), and * and x represent Hoogsteen and Watson-Crick hydrogen bonding patterns respectively. A novel recognition selectivity based on the orientation (parallel/antiparallel) of the third strand purines A, G or AP with A in the parallel motif (A(p)*U# x A), and G/AP in the antiparallel motif (G(ap)/AP(ap)*U# x A) is observed. Similarly for pyrimidines in the third strand, C is accepted only in a parallel mode (C(p)*U(#) x A). Significantly, T is recognised in both parallel and antiparallel modes (T(p)/T(ap)*U(#) x A), with the antiparallel mode being stable compared to the parallel one. The 'U(#)' triplexes are also more stable than the corresponding control 'T' triplexes. The results expand the lexicon of triplex triads with a recognition motif consisting of pyrimidine in the central strand.

Animals↗
PubMed1999

DNA-surfactant interactions: coupled cooperativity in ligand binding leads to duplex stabilization.

The cooperative nature of interaction of cationic surfactants with short oligonucleotides leading to eventual stabilization of DNA duplexes is demonstrated. At submicellar concentrations and DNA:surfactant charge ratios of 0.2 to 0.8, the association of single chain (CTAB) and double chain (DOTAP) surfactants to oligonucleotides is initiated by electrostatic interaction of cationic ligands with polyanionic DNA that aligns the surfactant molecules on the DNA template. This is followed by binding of new surfactant ligands to the initial complex, driven cooperatively by the hydrophobic forces, leading to in situ formation of surfactant-bound and bare duplexes as separate species. These exhibit independent melting behaviour characterised by double transition in thermal UV profiles, with a higher T(m) for surfactant-DNA complexes. Understanding the cooperative binding of the cationic surfactants to the DNA described here may have implications for rational design of DNA binding drugs and DNA delivery systems.

Base Sequence↗
PubMed1998

Thermodynamics of ligand (substrate/end product) binding to endoxylanase from Chainia sp. (NCL-82-5-1): isothermal calorimetry and fluorescence titration studies.

The binding of xylo-oligosaccharides to Chainia endoxylanase resulted in a decrease in fluorescence intensity of the enzyme with the formation of 1:1 complex. Equilibrium and thermodynamic parameters of ligand binding were determined by fluorescence titrations and titration calorimetry. The affinity of xylanase for the oligosaccharides increases in the order X2<X3<X4</=X5. Contributions from the enthalpy towards the free energy change decreased with increasing chain length from X2 to X4, whereas an increase in entropy was observed, the change in enthalpy and entropy of binding being compensatory. The entropically driven binding process suggested that hydrophobic interactions as well as hydrogen bonds play a predominant role in ligand binding.

Actinomycetales↗