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Biomedical subjects

T K Chaudhuri

Publications and source records attributed to T K Chaudhuri.

At least 19 recordsLinked to original sources
PubMed1999

Effect of the extra n-terminal methionine residue on the stability and folding of recombinant alpha-lactalbumin expressed in Escherichia coli.

The structure, stability, and unfolding-refolding kinetics of Escherichia coli-expressed recombinant goat alpha-lactalbumin were studied by circular dichroism spectroscopy, X-ray crystallography, and stopped-flow measurements, and the results were compared with those of the authentic protein prepared from goat milk. The electric properties of the two proteins were also studied by gel electrophoresis and ion-exchange chromatography. Although the overall structures of the authentic and recombinant proteins are the same, the extra methionine residue at the N terminus of the recombinant protein remarkably affects the native-state stability and the electric properties. The native state of the recombinant protein was 3.5 kcal/mol less stable than the authentic protein, and the recombinant protein was more negatively charged than the authentic one. The recombinant protein unfolded 5.7 times faster than the authentic one, although there were no significant differences in the refolding rates of the two proteins. The destabilization of the recombinant protein can be fully interpreted in terms of the increased unfolding rate of the protein, indicating that the N-terminal region remains unorganized in the transition state of refolding, and hence is not involved in the folding initiation site of the protein. A comparison of the X-ray structures of recombinant alpha-lactalbumin determined here with that of the authentic protein shows that the structural differences between the proteins are confined to the N-terminal region. Theoretical considerations for the differences in the conformational and solvation free energies between the proteins show that the destabilization of the recombinant protein is primarily due to excess conformational entropy of the N-terminal methionine residue in the unfolded state, and also due to less exposure of hydrophobic surface on unfolding. The results suggest that when the N-terminal region of a protein has a rigid structure, expression of the protein by E. coli, which adds the extra methionine residue, destabilizes the native state through a conformational entropy effect. It also shows that differences in the electrostatic interactions of the N-terminal amino group with the side-chain atoms of Thr38, Asp37, and Asp83 bring about a difference in the pKa value of the N-terminal amino group between the proteins, resulting in a greater negative net charge of the recombinant protein at neutral pH.

Animals↗
PubMed1998

Role of radionuclide phallogram in therapeutic decision-making for erectile dysfunction.

OBJECTIVE: The purpose of this study is to evaluate the role of radionuclide phallograms in therapeutic decision-making for erectile dysfunction. METHOD: Forty-eight impotent men being considered for pharmacologically-induced penile erection therapy (PIPE) had radionuclide phallograms (RP) as part of their evaluation. RP were performed using 99mTc-labeled autologous red blood cells and provided a measurement of penile blood volume (PBV) change following the intracorporeal injection of 0.25 to 0.3 mL of a papaverine/phentolamine mixture. RESULTS: Thirty-eight patients showed a good response with a mean PBV increase 2.6 times baseline (range 1.2 to 8.9). Ten patients had significantly lower PBV changes (P = 0.001) than the first group, with a mean PBV increase of 1.6 times baseline (range 1.1 to 2.4). These ten patients were dissatisfied with pharmacologically induced penile erection (PIPE) therapy after an unsuccessful treatment trial. CONCLUSION: We conclude that the RP can help to discriminate between patients who will benefit from PIPE therapy and those who will not.

Adult↗
PubMed1998

Pulmonary embolism and malpractice claims.

BACKGROUND: Deep venous thrombosis (DVT) with pulmonary embolization (PE) often occurs as an unexpected event with fatal consequences. This provides a setting for malpractice claims. METHODS: We reviewed 160 consecutive malpractice claims submitted by attorneys for medical expert review during the 11-year period ending in 1997. Seven cases involved DVT with PE. RESULTS: Alleged failure to anticipate and reduce the chance of PE was the basis for six of the claims. All six patients were at risk for lower extremity DVT, and one had a history of DVT 6 months earlier. The PE was manifested by sudden death in three cases. The seventh case represented a complication of heparin therapy for PE. CONCLUSIONS: We conclude that risk management for PE should focus primarily on DVT. Physicians should perform and document an examination for DVT whenever there is a history of lower extremity stasis or it is likely to occur. They should also consider documenting a concurring second opinion when making anticoagulant-related decisions.

Adult↗
PubMed1997

Refolding kinetics of partially reduced and S-carboxymethylated trypsin-subtilisin inhibitor from marine turtle eggwhite.

Three accessible disulphide bonds of basic trypsin-subtilisin inhibitor from marine turtle eggwhite have been reduced with 0.1M NaBH4 at 0 degree C under nitrogen atmosphere at pH9.8 and then S-carboxymethylated. The partially reduced inhibitor retains 80% of the native inhibitory activity towards trypsin and subtilisin. The S-carboxymethylated inhibitor undergoes slower refolding than the native inhibitor from its fully denatured and reduced state at pH 8.5 in the presence of oxidised and reduced glutathione. The refolding process was characterised by the attainment of the inhibitory activity towards trypsin and subtilisin. The values of the second order rate constant for the refolding reactions of the modified protein are 0.02 x 10(2)M-1sec1 and 0.033 x 10(2)M-1sec-1 for its trypsin and subtilisin inhibiting domains and their energies of activation are 20.1 Kcal/mole and 24.6 Kcal/mole. The partially modified inhibitor does not regain complete inhibitory activity even after long incubation in the oxido-shuffling buffer. From the above findings it can be concluded that the three disulphide bonds of the native inhibitor are not essential for the inhibitory activity of the trypsin-subtilisin inhibitor but they help in the correct refolding of the inhibitor by forming transient disulphide bonds with the external disulphide reagents as well as with the internal sulphydryl groups.

Animals↗
PubMed1997

Iatrogenic hypoglycemia and malpractice claims.

Iatrogenic neuroglycopenia represents a medical emergency for which accepted and usually effective treatment exists. Treating physicians face a malpractice risk if there is permanent neurologic damage and there is a perception of failure to act prudently both before and after the damaging episode. We report two cases to illustrate the medical and legal issues that may be raised in such claims.

Aged↗
PubMed1997

Stroke and malpractice claims.

We describe 15 malpractice claims that were filed after the patients had strokes. Both embolic and thrombotic, sterile and infected strokes led to claims. Ten of the claims alleged physician failure to protect the patient, two alleged physician failure to react as called for by symptoms, and three were related to medication. We conclude that physicians should advise patients of the possibility of stroke when circumstances warrant it, as well as documenting their judgment and suggested preventive practices. These cases further suggest that treatment decisions supported by documented second opinions may reduce the number of malpractice claims for strokes.

Anti-Bacterial Agents↗
PubMed1996

Refolding of trypsin-subtilisin inhibitor from marine turtle eggwhite.

Trypsin-subtilisin inhibitor from marine turtle eggwhite refolded quantitatively from its fully reduced state at pH 8.5 in the presence of reduced and oxidized glutathione. The refolding process was studied by following the accompanying changes in inhibitory activity, fluorescence, sulfhydryl group titer, and hydrodynamic volume. The refolding process followed second-order kinetics with rate constants of 4.80 x 10(2) M-1 sec-1 for trypsin-inhibiting domain and 0.77 x 10(2) M-1 sec-1 for subtilisin-inhibiting domain of the inhibitor at 30 degrees C and their respective activation energies of the refolding process were 15.9 and 21.6 kcal/mol. Fluorescence intensity of the reduced inhibitor decreased with time of refolding until it corresponded to the intensity of the native inhibitor. The inhibitor contained 1-2% alpha-helix, 40-42% beta-sheet, and 57-58% random coil structure. Refolded inhibitor gave a circular dichroic spectrum identical to that of the native inhibitor. A number of principal intermediates were detected as a function of the refolding time. Size-exclusion chromatography separated the intermediates differing in hydrodynamic volume (Stokes radius). The Stokes radius ranged from 23 A (fully reduced inhibitor) to 18.8 A (native inhibitor). Results indicated the independent refolding of two domains of the inhibitor and multiple pathways of folding were followed rather than an ordered sequential pathway.

Animals↗
PubMed1995

Medical characteristics of 61 unwarranted malpractice claims.

We describe malpractice claims closed by plaintiff attorneys after initial medical expert (ME) review. This retrospective study includes 61 cases, of which 33 originated in hospitals, 18 in physicians' offices, and 10 in nursing homes. No claims were against state or federal agencies. The reviews were done between 1987 and 1994 for 29 attorneys from 11 states. The cases fell into 12 diagnostic groups, and leading causes for action were late diagnosis (13 cases), drug administration (11 cases), sepsis (6 cases), and strokes (5 cases). We conclude that internists are particularly liable to unwarranted malpractice claims when unexpected complications occur and when treatment fails to cure infectious disease. However, such claims may be terminated following the initial ME review.

Accidental Falls↗
PubMed1995

Distribution of HLA antigens in Indian Gurkha population.

Fifty unrelated Indian Gurkha of Nepalese origin were studied to analyse the HLA antigen profile and their relation with other populations. Haplotype B35-Cw4 occurred with highest incidence and significant positive linkage disequilibrium in Gurkhas. Haplotype A10-B8 which occurs with the highest frequency in north Indians was also observed to occur with significant positive linkage in Gurkhas. HLA profile of Gurkhas thus may be the result of long-term isolation and genetic drift.

HLA Antigens↗
PubMed1994

Human monoclonal antibody developed against ovarian cancer cell surface antigen.

BACKGROUND: Murine monoclonal antibodies (MoAb) potentially can be used in the radioimmunodetection and radioimmunotherapy of cancer. However, the administration of these radiopharmaceuticals to humans often leads to induction of human anti-murine antibodies (HAMA). HAMA has many disadvantages, which could decrease efficacy of the murine MoAb. The purpose of this work was to produce human monoclonal antibody against a human ovarian cancer cell surface antigen (OCCSA), which was not present in normal ovarian cells. This 200-kilodalton OCCSA also was used in the present study for characterizing the human monoclonal antibody. METHODS: Human monoclonal antibodies were produced in vitro by fusion of mutant myeloma cells, selected from GM1500, with human lymphoid cells immunized in vitro with purified OCCSA: The human monoclonal antibody was characterized using the following techniques: sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), native-PAGE, Western blotting followed by protein-A gold staining, immunodiffusion assays, and fluorescent antibody assays. RESULTS: Human monoclonal antibody, TC5 (immunoglobulin G1), was produced and purified. It was found to be specific for ovarian cancer, while also reacting with an early stage breast cancer. TC5 did not react with any normal (i.e., nonneoplastic) cells of the ovary, uterus, cervix, endocervix, or fallopian tube, nor did it react with normal lung, heart, pancreas, liver, or breast tissue. CONCLUSION: Human-human hybridomas produced human monoclonal antibody against OCCSA: The human monoclonal antibody, TC5, was specific for ovarian and breast cancer. TC5 did not react with any normal tissue tested. Future work will focus on the in vivo characterization of the human monoclonal antibody, after labeling with radionuclides.

Antibodies, Monoclonal↗
PubMed1994

Detection of ovarian cancer by 198Au-labeled human monoclonal antibody.

BACKGROUND: There is no reliable method for the early diagnosis of ovarian cancer. Radiolabeled monoclonal antibodies have potential to assist in early diagnosis, but they are limited by problems that include antibody specificity, stability, and immunoreactivity, as well as patient reactions to the antibodies used. METHODS: Methods were developed to 198Au-label a human monoclonal antibody (TC5 antibody), developed against an ovarian cancer cell surface antigen. Antigen binding sites on the TC5 antibody were protected with sepharose 4B affinity chromatography before 198Au-labeling. The 198Au-labeled TC5 antibody was evaluated with biopsy specimens in a blind study. The immunoreactivity of radiolabeled TC5 antibody also was evaluated in slot-blot experiments with extracts of the biopsy specimens. RESULTS: The 198Au-labeled TC5 antibody had high binding reaction to all biopsy specimens (six of six) pathologically diagnosed as ovarian cancer (serous and endometrioid adenocarcinoma). The radiolabeled TC5 antibody did not bind to any normal (non-neoplastic) specimens (zero in ten), with one exception. One "normal" ovary specimen had high binding of radiolabeled TC5 antibody, and metastatic ovarian cancer was diagnosed 4 months later. The TC5 antibody labeled with 198Au, without protecting antigen-binding sites, did not bind to any biopsy specimens. CONCLUSIONS: The affinity-labeling method was necessary to protect antigen-binding sites and preserve the immunoreactivity of the TC5 antibody. The 198Au-labeling method may be an ideal technique to evaluate monoclonal antibodies in vitro. The TC5 antibody had high sensitivity and specificity for detecting ovarian cancer.

Antibodies, Monoclonal↗