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Biomedical subjects

A Sheth

Publications and source records attributed to A Sheth.

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

Superoxide dismutase in human testis preparations.

A protein fraction from human testis was structurally investigated. The main component of the fraction reported to contain inhibin-like activity was purified and analyzed by tryptic digestion. The peptides obtained identified the protein as an enzyme, superoxide dismutase, previously known to be present in seminal plasma. The results show that superoxide dismutase is a major enzyme, also of testicular material. They further demonstrate the importance of using pure fractions, and controls such as checks with structural analysis or synthetic peptides, in the work of elucidating the nature of inhibin and other hormonal peptides.

Amino Acid Sequence↗
PubMed1984

Analysis of an inhibin preparation reveals apparent identity between a peptide with inhibin-like activity and a sperm-coating antigen.

The amino acid sequence of a large form of inhibin-like peptide in human seminal plasma was determined, and compared with structures reported for similar inhibin preparations and a seminal plasma globulin. The data confirm and correlate previous reports on this form of inhibin-like peptide. The structural comparisons further suggest that the peptide is closely similar to or possibly identical to a sperm-coating antigen reported to be synthesized from prostatic epithelium. This may correlate with non-gonadal origins of inhibin-like material and will help to elucidate the biological roles of inhibin(s).

Amino Acid Sequence↗
PubMed1982

A randomized, double-blind study of two combined and two progestogen-only oral contraceptives.

A randomized double-blind study of two combined oral contraceptives and two progestogen-only oral contraceptives was conducted using the same protocol at WHO Collaborating Centres for Clinical Research in Human Reproduction in Bombay and Ljubljana of the 518 women admitted to the trial, 123 received mestranol 50 micrograms + norethisterone 1mg (MES 50 + NET 1); 137 received ethinyl estradiol 30 micrograms + levonorgestrel 150 micrograms (EE 30 + LNG 150); 130 received norethisterone 350 micrograms/NET 350); and 128 received levonorgestrel 30 micrograms (LNG 30). At one year, between 52.6 and 61.0 percent of those recruited had discontinued oral contraceptive use for all reasons, and by two years, between 70.5 and 76.5 percent had discontinued the treatment. These rates did not differ between the four treatment groups. However, discontinuation rates for all medical reasons at one and two years, and at two years pregnancy rates and discontinuation rates for bleeding disturbances, were significantly lower in the EE/LNG preparation. The groups receiving the MES/NET, LNG and NET had similar pregnancy rates, discontinuation rates for all medical reasons and all bleeding disturbances. There were two ectopic pregnancies among the 22 pregnancies in the progestogen-only groups. Discontinuation because of headache, dizziness and other central nervous system symptoms were significantly more common in those receiving MES/NET compared to EE/LNG. In contrast, discontinuation for gastro-intestinal disturbances were significantly higher in the EE/LNG combined preparation. Bleeding disturbances in the first few cycles tended to be higher in NET than in the LNG group. The data suggest that greater consideration be given to the benefits and risks of including progestogen-only oral contraceptives in the family planning programmes of some countries.

Adolescent↗
PubMed1981

Evidence for active and passive urate transport in the rat proximal tubule.

Studies utilizing the technique of simultaneous microperfusion of peritubular capillaries and tubular lumen of the proximal tubule of the rat were performed to determine if the absorption of urate was an active transport process and to determine the passive permeability coefficient for urate. When radioactive urate of equal specific activity and concentration was present in both perfusion solutions, the ratio of collected to initial concentrations of urate in the luminal perfusate (CO/CI) was 0.71 +/- 0.02. This gradient was higher than that predicted at equilibrium from the electrical potential difference determined in the in vitro perfused rabbit proximal tubule. The addition of para-chloromercuribenzoate (PCMB) to both solutions resulted in a significantly higher CO/CI of 0.90 +/- 0.02. This latter value is closer to the value predicted at electrochemical equilibrium. In separate studies, the unidirectional fluxes of urate were determined in the presence of PCMB. The calculated passive permeability coefficient averaged approximately 0.94 pmol . min-1 . mm-1 . mM-1 and was equal in both directions. These results indicate that in the rat proximal tubule urate absorption is an active transport process. In addition, there exists a passive permeation pathway for urate movement out of and into the proximal tubule.

Animals↗
PubMed1979

Serum gonadotropins and testosterone in infertile patients with varicocele.

Serum concentrations of gonadotropins and testosterone in 25 infertile men with varicocele were compared with those in control men and men with idiopathic oligo-azoospermia. No significant difference was found in values of serum follicle-stimulating hormone (FSH) (14.9 +/- 13.6 mIU/ml), luteinizing hormone (LH) (24.9 +/- 19.1 mIU/ml), and testosterone (5.0 +/- 2.1 ng/ml) when the group with varicocele was compared with either the control group (FSH, 7.0 +/- 3.2 mIU/ml; LH, 23.6 +/- 16.0 mIU/ml; testosterone, 5.3 +/- 1.8 ng/ml) or the group with idiopathic oligo-azoospermia (FSH, 23.0 +/- 22.69 mIU/ml; LH, 36.7 +/- 24.1 mIU/ml; testosterone, 5.31 +/- 2.3 ng/ml). However, compared with the control group, there was a significant elevation of serum FSH levels in patients with varicocele whose testicular biopsy score counts were between 1 and 4. The importance of preoperative determination of the serum FSH level is discussed.

Biopsy↗
PubMed1978

Clobazam versus diazepam--a double-blind study in anxiety neurosis.

Clobazam, a new antianxiety compound, was compared in a double-blind study with diazepam in 40 neurotic outpatients. Twenty-three patients completed the trial under clobazam conditions while 17 patients completed the trial under diazepam conditions. The trial was conducted for a period of four weeks of active drug administration followed by a one-week period of placebo administration. Clobazam was administered in three divided doses of 30 to 40 mg/day, while diazepam was administered in three divided doses of 15 to 20 mg/day, following a fixed dosage schedule. No significant differences were noted between the two treatment conditions during the drug trial period. The patients on clobazam maintained greater improvement during the placebo trial period for the variables "somatic anxiety" and "nights of sleep disturbance." Simultaneous motor coordination tests (hand steadiness test) showed greater improvement on clobazam throughout the trial period in patients with an initial error score greater than 50 points. This difference was significant during the second week of the trial.

Adult↗