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Biomedical subjects

S Yadav

Publications and source records attributed to S Yadav.

At least 37 records · Page 2Linked to original sources
PubMed2000

A new method for the determination of stability parameters of proteins from their heat-induced denaturation curves.

A new method has been developed for determining the stability parameters of proteins from their heat-induced transition curves followed by observation of changes in the far-UV circular dichroism (CD). This method of analysis of the thermal denaturation curve of a protein gave values of stability parameters that not only are identical to those measured by the differential scanning calorimetry (DSC), but also are measured with the same error as that observed with a calorimeter. This conclusion has been reached from our studies of the reversible heat-induced denaturation of lysozyme and ribonuclease A at various pH values. For each protein, the conventional method of analysis of the conformational transition curve, which assumes a linear temperature dependence of the pre- and posttransition baselines, gave the estimate of DeltaH(van)(m) (enthalpy change on denaturation at T(m), the midpoint of denaturation) which is significantly lower than DeltaH(cal)(m), the value obtained from DSC measurements. However, if the analysis of the same denaturation curve assumes that a parabolic function describes the temperature dependence of the pre- and posttransition baselines, there exists an excellent agreement between DeltaH(van)(m) and DeltaH(cal)(m) of the protein. The latter analysis is supported by the far-UV CD measurements of the oxidized ribonuclease A as a function of temperature, for the temperature dependence of this optical property of the protein is indeed nonlinear. Furthermore, it has been observed that, for each protein, the constant-pressure heat capacity change (DeltaC(p)) determined from the plots of DeltaH(van)(m) versus T(m) is independent of the method of analysis of the transition curve.

Animals↗
PubMed2000

A possible origin of differences between calorimetric and equilibrium estimates of stability parameters of proteins.

To test the validity of thermodynamic parameters from the equilibrium method, we have studied the reversible heat-induced denaturations of lysozyme, ribonuclease A, cytochrome c and myoglobin at various pH values, using absorption spectral measurements. For each protein, if a linear temperature-dependence of the pre- and post-transition baselines is assumed for the analysis of the conformational-transition curve, the estimate of DeltaH (the enthalpy change on denaturation at T(m), the midpoint of denaturation) is significantly less than DeltaH, the value obtained by the calorimetric measurements. If the analysis of thermal-denaturation curves assumes that the temperature-dependence of pre- and post-transition baselines is described by a parabolic function, there exists an excellent agreement between DeltaH(m) values of all proteins obtained from equilibrium and calorimetric methods. The latter analysis is supported by the studies on model compounds, for measurements of absorption properties of tyrosine, tryptophan and haem as a function of temperature suggested that the temperature-dependencies of the optical properties are indeed non-linear. We have observed that for each protein the constant-pressure heat-capacity change on denaturation (DeltaC(p)) determined from the plots of DeltaH versus T(m) is not only independent of the method of analysis of the transition curve, but it is also in excellent agreement with calorimetric DeltaC(p). An important conclusion of this study is that for these proteins that exhibit two-state character, all stability parameters are measured with the same error as that observed with a calorimeter.

Biochemistry↗
PubMed2000

Teaching residents evidence-based medicine skills: a controlled trial of effectiveness and assessment of durability.

OBJECTIVES: To measure the effectiveness of an educational intervention designed to teach residents four essential evidence-based medicine (EBM) skills: question formulation, literature searching, understanding quantitative outcomes, and critical appraisal. DESIGN: Firm-based, controlled trial. SETTING: Urban public hospital. PARTICIPANTS: Fifty-five first-year internal medicine residents: 18 in the experimental group and 37 in the control group. INTERVENTION: An EBM course, taught 2 hours per week for 7 consecutive weeks by senior faculty and chief residents focusing on the four essential EBM skills. MEASUREMENTS AND MAIN RESULTS: The main outcome measure was performance on an EBM skills test that was administered four times over 11 months: at baseline and at three time points postcourse. Postcourse test 1 assessed the effectiveness of the intervention in the experimental group (primary outcome]; postcourse test 2 assessed the control group after it crossed over to receive the intervention; and postcourse test 3 assessed durability. Baseline EBM skills were similar in the two groups. After receiving the EBM course, the experimental group achieved significantly higher postcourse test scores (adjusted mean difference, 21%; 95% confidence interval, 13% to 28%; P < .001). Postcourse improvements were noted in three of the four EBM skill domains (formulating questions, searching, and quantitative understanding [P < .005 for all], but not in critical appraisal skills [P = .4]). After crossing over to receive the educational intervention, the control group achieved similar improvements. Both groups sustained these improvements over 6 to 9 months of follow-up. CONCLUSIONS: A brief structured educational intervention produced substantial and durable improvements in residents' cognitive and technical EBM skills.

Adult↗
PubMed2000

Protective effects of ischemic preconditioning for liver resection performed under inflow occlusion in humans.

OBJECTIVE: To determine whether ischemic preconditioning protects the human liver against a subsequent period of ischemia in patients undergoing hemihepatectomy, and to identify possible underlying protective mechanisms of ischemic preconditioning, such as inhibition of hepatocellular apoptosis. SUMMARY BACKGROUND DATA: Ischemic preconditioning is a short period of ischemia followed by a brief period of reperfusion before a sustained ischemic insult. Recent studies in rodents suggest that ischemic preconditioning is a simple and powerful protective modality against ischemic injury of the liver. The underlying mechanisms are thought to be related to downregulation of the apoptotic pathway. METHODS: Twenty-four patients undergoing hemihepatectomy for various reasons alternatively received ischemic preconditioning (10 minutes of ischemia and 10 minutes of reperfusion) before transection of the liver performed under inflow occlusion for exactly 30 minutes. Liver wedge and Tru-cut biopsy samples were obtained at the opening of the abdomen and 30 minutes after the end of the hepatectomy. Serum levels of aspartate transferase, alanine transferase, bilirubin and prothrombin time were determined daily until discharge. Hepatocellular apoptosis was evaluated by in situ terminal deoxynucleotidyl transferase mediated d-UTP nick end-labeling (TUNEL) assay and electron microscopy. Caspase 3 and 8 activities were measured in tissue using specific fluorometric assays. RESULTS: Serum levels of aspartate transferase and alanine transferase were reduced by more than twofold in patients subjected to ischemic preconditioning versus controls. The analysis of a subgroup of patients with mild to moderate steatosis indicated possible increased protective effects of ischemic preconditioning. In situ TUNEL staining demonstrated a dramatic reduction in the number of apoptotic sinusoidal lining cells in the ischemic preconditioning group. Electron microscopy confirmed features of apoptosis present in control but not in ischemic preconditioning patients. There was no significant difference in caspase 3 and 8 activity when patients with ischemic preconditioning were compared with controls. CONCLUSIONS: Ischemic preconditioning is a simple and effective modality protecting the liver against subsequent prolonged periods of ischemia. This strategy may be a more attractive technique than intermittent inflow occlusion, which is associated with increased blood loss during each period of reperfusion.

Adult↗
PubMed2000

Structure of buffalo lactoferrin at 3.3 A resolution at 277 K.

The three-dimensional structure of diferric buffalo lactoferrin has been determined at 3.3 A resolution. The structure was solved by molecular replacement using the coordinates of diferric human lactoferrin as a search model and was refined by simulated annealing (X-PLOR). The final model comprises 5316 protein atoms for all 689 residues, two Fe(3+) and two CO(3)(2-) ions. The final R factor was 21.8% for 11 711 reflections in the resolution range 17.0-3.3 A. The folding of buffalo lactoferrin is essentially similar to that of the other members of the transferrin family. The significant differences are found in the dimensions of the binding cleft and the interlobe orientation. The interlobe interactions are predominantly hydrophobic in nature, thus facilitating the sliding of two lobes owing to external forces. The interdomain interactions are comparable in the N and C lobes.

Amino Acid Sequence↗
PubMed1999

A new cardenolide uzarigenen-3-O-beta-D-xylopyranosyl (1-->2)-alpha-L-rhamnopyranoside.

A new cardenolide C34H52O12, m.p. 225-226 degrees C, [M+ -H] 651 (EIMS) was isolated from the acetone soluble fraction of the concentrated 90% ethanolic extracts of the seeds of Tamarindus indica (Linn.). It was identified as uzarigenin-3-O-beta-D-xylopyranosyl (1 -->2)- alpha-L-rhamnopyranoside (I) by different colour reactions, chemical degradations and spectral analysis.

Cardenolides↗
PubMed1999

Structure of buffalo lactoferrin at 2.5 A resolution using crystals grown at 303 K shows different orientations of the N and C lobes.

The structure of buffalo lactoferrin has been determined at 303 K. The crystals belong to orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 77.5, b = 91.0, c = 131.5 A and Z = 4. The structure has been refined to an R factor of 0.187. The overall structure of the protein is similar to its structure determined at 277 K in a different crystal form. However, the lobe orientations in the two structures differ by 9.0 degrees, suggesting significant inter-lobe flexibility in this family of proteins. The inter-lobe interactions are predominantly hydrophobic and could act as a cushion for a change in orientation under the influence of external conditions. On the other hand, the domain arrangements are found to be similar in 277 and 303 K crystal structures, with orientations differing by 1.5 and 1.0 degrees in the N and C lobes, respectively. The results of these investigations suggest that the increase in temperature helps in the production of better quality crystals.

Animals↗
PubMed1999

Evaluation of serological status of rubella & mumps in children below five years.

A cross-sectional study was carried out on 321 serum samples to detect rubella and mumps antibodies in children below five years and to assess the optimum age for immunization against rubella and mumps. Seropositivity to rubella was 33.3 per cent in children below nine months, 16.9 per cent at 9-12 months and 25.5 per cent by two years. Mean antibody levels for rubella were low at nine months to one year and remained so till five years of age. Similarly, seropositivity for mumps was 53.3 per cent below nine months, 20.3 per cent at 9-12 months and 40 per cent by two years. Mean antibody levels for mumps were low between nine months to two years with a slight rise by five years. The findings suggest that a large majority of children are at risk by the age of nine months in our population and the measles, mumps and rubella (MMR) vaccination at this age may be most beneficial.

Antibodies, Viral↗
PubMed1998

Arterial haemorrhage following instillation of silver nitrate in chyluria: treatment by coil embolization.

Chyluria is a urological manifestation of lymphatic system disease. Sclerotherapy of the renal pelvis (RPIS) using 1% silver nitrate, along with diethyl carbamazine, is the treatment most frequently used. Massive haematuria due to intrarenal aneurysm following RPIS has not been reported. A case is described here of arterial haemorrhage following instillation of silver nitrate which was treated by coil embolization. The haematuria was immediately stopped and the renal function returned to normal gradually.

Adult↗
PubMed1998

Estimation of fasting and post oral glucose serum insulin levels in hypertensive and obese subjects.

Insulin resistance and consequent hyperinsulinemia has been documented as a frequent occurrence in hypertension and obesity. Fasting and post oral glucose serum insulin levels serve as reliable markers of the state of insulin resistance. In this study, fasting serum insulin levels, as measured by radio-immunoassay method, were found to be more increased in obese individuals than in those with hypertension alone. While, post-oral glucose load serum insulin levels increased more in hypertensive individuals than those with obesity alone. In subjects who had obesity and hypertension together, the fasting serum insulin levels did not show much change while post oral glucose load serum insulin levels greatly increased suggesting a compounding effect.

Adult↗