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Biomedical subjects

G Govil

Publications and source records attributed to G Govil.

At least 37 records · Page 2Linked to original sources
PubMed1992

Maturation of rat spermatozoa: ESR spin labeling studies.

The ability of spermatozoa to reduce nitroxide spin--TEMPO has been used as a parameter to understand maturation, capacitation and calcium uptake of sperm obtained from Holstman strain rats. The rate of spin label reduction by sperm follows the trend--caput greater than cauda greater than corpus. With the increase in age, the electron donating capability shows first a gradual increase, for 60- to 85-day-old rats, peaking at 85 days (corresponding to puberty) and leveling off after 92 days. Calcium uptake takes place in two phases which corresponds to accumulation of and activation by calcium. The presence of polyclonal antibody which is known to cause agglutination, does not adversely affect the sperm activity.

Animals↗
PubMed1991

Torsion angle approach to nucleic acid distance geometry: TANDY.

An efficient algorithm for generating DNA structures from a given set of distance constraints has been developed. The present implementation is suited for single-stranded DNA. The performance of the program has been tested with constraint sets representative of most stringent theoretical cases and also with usually available experimental ones. The results indicate that use of NOE-derived constraints alone generates an extremely large family of conformers and suggest that the quality of structure determination may be enhanced by incorporating additional constraints obtained by other means. The speed of the program makes it ideal for interactive use in conjunction with other complementary algorithms such as those for spectral simulation, energy minimization and molecular dynamics calculations.

Algorithms↗
PubMed1991

Glucose oxidase immobilized electrode for potentiometric estimation of glucose.

Glucose oxidase has been immobilized onto a thin platinum strip, by co-crosslinking with bovine serum albumin and glutaraldehyde. The retention of redox characteristics of glucose oxidase has been verified by cyclic voltammetry. The activity of the immobilized enzyme reduces to a quarter of its value when the enzyme is in solution but improves when coimmobilized with 1 M urea. The potentiometric response builds up and remains stable after 100 s. It is sensitive to the thickness of the immobilizing matrix. pH and temperature. An improvement in the performance of the electrode has been achieved by co-immobilizing 2 M urea and metal ions such as Mg2+ and Mn2+. The presence of Cu has been proved to be detrimental. The electrode has been calibrated in the 0.1-5.0 mM glucose concentration range. It gives a stable response for more than 50 independent assays and can be stored for 60 days without significant loss of function.

Biosensing Techniques↗
PubMed1990

Glycolysis and Entner-Doudoroff pathways in Halobacterium halobium: some new observations based on 13C NMR spectroscopy.

13C NMR was used to study glucose metabolism in intact cells of Halobacterium halobium. Spectra of glucose grown cells incubated with [1-13C] glucose indicate the presence of gluconate as the initial product. The existence of glycolytic pathway is also indicated. In the extracts of these cells an NADP dependent glucose dehydrogenase was detected. Galactose grown cells failed to metabolise glucose but exhibited glucose dehydrogenase activity although about 20-50% less than that for glucose grown cells. Possible explanations of these experiments are discussed.

Carbon Isotopes↗
PubMed1990

Solvent induced conformational changes in renin inhibitor polypeptide.

Conformation of the renin inhibitor peptide, Pro-His-Pro-Phe-His-Phe-Phe-Val-Tyr-Lys (RIP) has been studied in aqueous solution and in lipid bilayers using 500 MHz 1H NMR spectroscopy. Analysis of the NMR parameters indicates that in aqueous solution, RIP exists as a random coil. On incorporation into lipid bilayers, the peptide adopts a rigid and well defined conformation. The N-terminal end is stabilized by the hydrophobic environment of the lipid bilayer. The C-terminal end is located near the lipid-water interface and attains rigidity due to interaction with the phosphate groups of lipids. The observations emphasize the role of environment in stabilizing significantly different conformations of RIP in three different media--D2O, DMSO and lipid bilayers.

Amino Acid Sequence↗
PubMed1989

Solution conformation of d-CTCGAGCTCGAG by two-dimensional NMR: conformational heterogeneity at XhoI cleavage site.

Nonexchangeable proton resonances in the 500-MHz NMR spectrum of d-CTCGAGCTCGAG have been assigned by using two-dimensional correlated spectroscopy (COSY) and nuclear Overhauser enhancement spectroscopy (NOESY). 1H-1H coupling constants (J) in the deoxyribose rings have been measured by analyzing intensity and multiplet patterns in the phase-sensitive omega 1-scaled COSY spectra. A modification of the J-resolved technique, called amplitude-modulated J-resolved spectroscopy, has been described and used to increase the accuracy of J measurements. Absorption mode omega 1-scaled NOESY spectra at mixing times in the range 50-200 ms have been analyzed to monitor spin diffusion. A 50-ms spectrum has been used to estimate several interproton distances. The coupling constant and distance data have been used to arrive at sequence-specific sugar geometries and glycosidic torsion angles. The backbone structure has been refined by model building using the FRODO program, employing the sugar geometries and glycosidic torsion angles discussed above. The molecule shows interesting sequence-dependent variations in the structure. The cleavage site of the restriction enzyme XhoI exhibits unique differences in the sugar geometry and backbone torsion angles.

Base Sequence↗
PubMed1989

Quantification of DNA structure from NMR data: conformation of d-ACATCGATGT.

Resonance assignments of nonexchangeable base and sugar protons have been obtained in double-helical d-ACATCGATGT by using two-dimensional correlated spectroscopy (COSY) and nuclear Overhauser enhancement spectroscopy (NOESY). The exchangeable imino protons have been assigned on the basis of their chemical shifts. The characteristic phase-sensitive multiplet patterns of the intrasugar cross-peaks in the omega 1-scaled COSY spectrum have been used to estimate several scalar coupling constants (J). The information on the J values combined with the intranucleotide COSY cross-peak intensities has been used to identify sugar puckers of individual nucleotide units. In most cases, the deoxyribofuranose rings are found to adopt a conformation close to O4'-endo. Spin diffusion has been monitored from the buildup of the normalized volumes of NOE cross-peaks in NOESY spectra as a function of mixing time. A set of 52 intranucleotide and internucleotide proton-proton distances have been estimated by using low mixing time NOESY spectra (tau m = 40 and 80 ms). The estimated intrasugar proton-proton distances rule out possibilities of existence of a fast equilibrium between C2'-endo and C3'-endo conformations. Intranucleotide proton-proton distances combined with the knowledge of sugar puckers have been used to fix the glycosidic bond torsion angle (chi). For this purpose, simulated distance contours depicting the dependence of intranucleotide proton-proton distances on pseudorotational phase angle (P) and glycosidic bond torsion angle (chi) have been used. Further, the proton homonuclear (J, delta) spectrum has been used to monitor the 31P-1H heteronuclear couplings, which are preserved in the omega 2 projection.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Composition↗
PubMed1988

Sequence-specific solution structure of d-GGTACGCGTACC.

Complete resonance assignments of nonexchangeable base protons and sugar protons in d-GGTACGCGTACC at 500 MHz have been obtained by two-dimensional correlated spectroscopy (COSY) and nuclear Overhauser enhancement spectroscopy (NOESY). The characteristic phase-sensitive multiplet patterns of the ntrasugar cross peaks in the omega 1-scaled COSY spectrum have been used to estimate several scalar coupling constants (J). These coupling constants combined with the intranucleotide COSY cross peak intensities have been used to identify the sugar pucker of individual nucleotide units. In most cases, the deoxyribose rings adopt a conformation close to O4'-endo. Spin-diffusion has been monitored from the buildup of the normalized volumes of NOE cross peaks in NOESY spectra as a function of mixing time. A set of 55 intranucleotide and internucleotide interproton distances have been estimated from the low mixing time NOESY spectrum (tau m = 75 ms). The estimated intranucleotide proton-proton distances have been used to determine the individual glycosidic dihedral angles of the nucleotide units which lie in the anti domain. It is observed that the molecule adopts an overall conformation close to that of the B-form although there are differences in the intricate details.

Base Sequence↗
PubMed1988

Magnetic resonance studies of intact human spermatozoa.

A correlation has been established between the ability of sperms to reduce the nitroxide spin label--TEMPO and their metabolic activity. The rate of reduction of TEMPO is sensitive to the quantity and quality of sperms and therefore, this property can be developed into a quality rating method. Keeping this in mind, effects of various agents on the spin label reduction rates have been studied. The effect of cold shock on sperms has been found to be harmless and does not lead to loss in metabolic activity. The differential rates of spin label reduction after bubbling N2 and O2 gases through the samples indicate that the process of anaerobic glycolysis imparts higher electron donating capacity to spermatozoa. The method has been used to study influence of inhibitors of electron transport chain (ETC) such as rotenone, antimycin A, KCN and sodium azide which inhibit ETC at different levels.

Antimycin A↗
PubMed1987

Two dimensional NMR studies on the solution structure of d-CTCGAGCTCGAG.

Two dimensional (2D) FT-NMR investigations have been carried out on the self-complementary dodecanucleotide d-CTCGAGCTCGAG, which has cleavage sites for the restriction enzyme Xho I (between C and T). The central TCG portion is also known to show a preference for DNAase activity. Complete resonance assignments have been obtained for the non-exchangeable sugar and base protons of the oligonucleotide. Information regarding sugar geometries, glycosidic torsion angles and other structural parameters has been obtained from the relative intensities of the cross peaks in the COSY and NOESY spectra. The results indicate that deoxyribose rings of C1 and C7 adopt a conformation different from the remaining sugars in the double helical oligonucleotide. The central TCG portion also exhibits variations in the backbone structure. The base stacking in the double helix shows interesting sequence dependent effects suggesting that the sequence effects are not localised to nearest neighbours but extended over longer stretches.

Base Sequence↗
PubMed1987

Novel solution conformation of DNA observed in d(GAATTCGAATTC) by two-dimensional NMR spectroscopy.

Resonance assignments of nonexchangeable base and sugar protons of the self-complementary dodecanucleotide d(GAATTCGAATTC) have been obtained by using the two-dimensional Fourier transform NMR methods correlated spectroscopy and nuclear Overhauser effect spectroscopy. Conformational details about the sugar pucker, the glycosidic dihedral angle, and the overall secondary structure of the molecule have been derived from the relative intensities of cross peaks in the two-dimensional NMR spectra in aqueous solution. It is observed that d(GAATTCGAATTC) assumes a novel double-helical structure. The solution conformations of the two complementary strands are identical, unlike those observed in a related sequence in the solid state. Most of the five-membered sugar rings adopt an unusual O1'-endo geometry. All the glycosidic dihedral angles are in the anti domain. The AATT segments A2-T5 and A8-T11 show better stacking compared to the rest of the molecule. These features fit into a right-handed DNA model for the above two segments, with the sugar geometries different from the conventional ones. There are important structural variations in the central TCG portion, which is known to show preferences for DNase I activity, and between G1-A2 and G7-A8, which are cleavage points in the EcoRI recognition sequence. The sugar puckers for G1 and G7 are significantly different from the rest of the molecule. Further, in the three segments mentioned above, the sugar phosphate geometry is such that the distances between protons on adjacent nucleotides are much larger than those expected for a right-handed DNA. We suggest that such crevices in the DNA structure may act as "hot points" in initiation of protein recognition.

Deoxyribose↗
PubMed1987

Magnetic resonance studies on the binding of etomidate to lipid bilayers.

Physicochemical studies on the binding of etomidate, a fast acting anaesthetic, with lipid bilayers have been carried out. ESR spin labeling studies indicate that the gel to liquid crystalline phase transition of dipalmitoyl phosphatidyl choline (DPPC) vesicles retains its cooperative nature on incorporation of the anaesthetic. For a 5:1 lipid to drug molar ratio, the phase transition occurs at an unusually lower temperature than those observed with other drug-DPPC systems. Results of 13C NMR and 1H NOE experiments suggest that the drug molecules reside in the close proximity of the terminal of hydrocarbon chains of the lipid molecules. 31P NMR and Electron Microscopic experiments indicate that the presence of etomidate alters the normal lamellar structure of DPPC vesicles into hexagonal (HII) type. Based on these observations, a model for drug-lipid binding has been proposed.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1986

A novel structure observed in d-GAATTCCCGAATTC by 2D NMR.

Sequential resonance assignments of the non exchangeable base and sugar protons in d-GAATTCCCGAATTC have been obtained using two dimensional NMR experiments at 500 MHz. The chemical shifts and the NOEs have been used to determine the structure in the base-pair mismatch region which is located in the central portion of the molecule. It is observed that the molecule adopts a novel unsymmetrical loop structure in this section which is characterised by sugar geometries which are significantly different compared to the rest of the molecular. The base-paired portion of the molecule conforms to a right handed B-DNA type of structure.

Base Sequence↗
PubMed1986

Solution structure of d-GAATTCGAATTC by 2D NMR. A new approach to determination of sugar geometries in DNA segments.

A new approach based on the correlated spectroscopy (COSY) in 2D NMR has been described for determination of sugar geometries in oligonucleotides. Under the usual low resolution conditions employed in COSY, the intensities of cross peaks depend on the magnitudes of coupling constants. There are five vicinal coupling constants in a deoxyribose ring which are sensitive to the sugar geometry. The presence, absence and rough comparison of relative intensities of COSY cross peaks arising from such coupling constants enable one to fix the sugar conformation to a fair degree of precision. The methodology has been applied to d-GAATTCGAATTC. It is observed that ten out of the twelve nucleotide units in this sequence exhibit a rare O1'-endo geometry. The EcoRI cleavage sites (between G and A) in the dodecanucleotide show an interesting variation in the conformation with the two sugars attached to the Gs acquiring a geometry between C2'-endo and C4'-endo.

Carbohydrate Conformation↗
PubMed1986

Molecular conformation of gonadoliberin using two-dimensional NMR spectroscopy.

Complete resonance assignments of the proton NMR spectrum of gonadoliberin (in its native amide and free acid forms) have been obtained using two-dimensional nuclear magnetic resonance spectroscopy under three different environmental conditions, namely, dimethyl sulphoxide solution, aqueous solution and lipid-bound form in model membranes. The proton chemical shifts in the three cases have been compared to derive information about inherent conformational characteristics of the molecule. It has been inferred that the molecule possesses no short-range or long-range order under any of the three solvent conditions. However, there is a nonspecific increase in the linewidths when gonadoliberin is bound to model membranes, indicating a reduced internal motion in the molecule due to lipid-peptide interactions.

Deuterium↗
PubMed1985

Resonance assignment of the 500-MHz proton NMR spectrum of self-complementary dodecanucleotide d-GGATCCGGATCC: altered conformations at BamHI cleavage sites.

Resonance assignments of nonexchangeable base and sugar protons of the self-complementary dodecanucleotide d-GGATCCGGATCC have been obtained by two-dimensional NMR methods and strategies derived from interproton distance calculations on different secondary structures of nucleic acids. Conformational details about the glycosidic dihedral angle and sugar pucker have been derived from the relative intensities of cross peaks in the two-dimensional J-correlated and nuclear Overhauser enhancement correlated spectra in D2O solution. It is observed that d-GGATCCGGATCC assumes a predominantly B-type conformation with sequence-dependent changes along the chain. The recognition site of BamHI shows a distinctly different geometrical environment. The sugar rings of G1 and G7 assume a C3'-endo geometry while the rest of the sugars possess C2'-endo geometry.

Base Sequence↗