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Biomedical subjects

P Bhattacharya

Publications and source records attributed to P Bhattacharya.

At least 55 records · Page 3Linked to original sources
PubMed1994

X-syndrome: is there impairment of myocardial perfusion during stress?

Stress T1-201 myocardial scintigraphy was carried out in 16 patients with x-syndrome. Eleven patients having IHD with single-vessel disease served as the control. With bicycle exercise test all 16 patients with x-syndrome had some type of myocardial perfusion abnormality. These perfusion defects were situated in the vascular beds of different coronary arteries. Myocardial perfusion defects in patients with x-syndrome were similar to those patients with moderate, but haemodynamically significant, single-vessel disease. At the same time, these perfusion defects were significantly less pronounced than those in patients with a subtotal occlusion of one coronary artery. Thus, patients with x-syndrome have not only the clinical features of IHD (anginal attacks), but also marked stress-induced, myocardial perfusion defects.

Angina Pectoris↗
PubMed1993

An endoribonuclease activity associated with Lettre Ehrlich ascites tumor cell mitochondria.

The splicing of 3.36kb mouse mitochondrial mRNA precursor(L-strand) to 69bp RNA component is shown to be mediated by an endoribonuclease activity associated with Lettre Ehrlich ascites tumor cell mitochondria. The enzymic activity was partially purified by column chromatography and the in vitro reconstituted RNA processing assay was performed to document this finding.

Animals↗
PubMed1991

Specificity of antitermination mechanisms. Suppression of the terminator cluster T1-T2 of Escherichia coli ribosomal RNA operon, rrnB, by phage lambda antiterminators.

Transcription of the ribosomal RNA operons (rrn) in Escherichia coli is subject to an antitermination mechanism whereby RNA polymerase is modified to a termination-resistant form during transit through the rrn leader region. This antitermination mechanism is unable to overcome the T1-T2 terminator cluster located at the end of an rrn operon, such as rrnB. We have tested the specificity with which the T1-T2 terminators override an antitermination mechanism, by placing the terminator cluster downstream from the nut and qut sites recognized by phage lambda N and Q gene antiterminators, respectively. Measurement of downstream gene expression shows that RNA polymerase modified by either N or Q reads through the T1-T2 terminators quite efficiently. This supports the view that T1-T2 are not superterminators, and that the rrn antitermination mechanism may have a restricted terminator specificity.

Bacteriophage lambda↗
PubMed1991

A DNA binding domain is contained in the C-terminus of wild type p53 protein.

In the present study we evaluated the DNA binding activity of wild type and mutant p53 proteins that were isolated from bacterial expression vectors. A comparison of the binding activities of the various purified p53 proteins, assessed by their ability to bind DNA cellulose columns, indicated that wild type p53 has a higher affinity to DNA than have mutant p53 forms. Furthermore, only wild type p53 was able to bind genomic DNA upon electrophoretic protein blotting. As specific deletion of the C-terminal region of wild type p53 totally abolished binding to genomic DNA, it was concluded that the 47 C-terminal amino acids contain the DNA binding region. The fact that the N-terminus contains a transcription activation region whereas the C-terminus contains a DNA binding domain places p53 in the family of typical transcription factors. Our experiments show that the topographical positioning of these domains plays an important role in the activity of wild type p53.

Amino Acid Sequence↗
PubMed1988

Characterization of a protein C activator from the venom of Agkistrodon contortrix contortrix.

An enzyme capable of activating protein C has been purified 60-fold from the venom of the Southern copperhead snake (Agkistrodon contortrix) by ion-exchange and gel filtration chromatography. The purified enzyme consists of a single polypeptide with an apparent molecular weight of 37,000. The isoelectric point of the protein C activator was determined to be 6.3 when measured by chromatofocusing. The enzyme was inhibited by p-nitrophenyl p-guanidinobenzoate, phenylmethanesulfonyl fluoride, and D-Phe-Pro-Arg-CH2Cl but was not affected by cysteine-directed reagents or by metal chelators. These results suggest that the enzyme is a serine protease. Protein C activator was capable of hydrolyzing the thrombin substrate tosyl-Gly-Pro-Arg-p-nitroanilide (TGPRpNA), and steady-state kinetic studies determined that the Km for amidolysis of this substrate was 1.1 mM while the Vmax was 66 s-1. The activator demonstrated considerable substrate specificity since the amidolysis of D-Phe-Pip-Arg-pNA, D-Ile-Pro-Arg-pNA, Bz-Ile-Glu-Gly-Arg-pNA, D-Val-Leu-Arg-pNA, and pyrGlu-Pro-Arg-pNA was less than 10% of that of TGPRpNA when measured under identical conditions using 1.0 mM substrate concentrations. The enzyme appears to be thrombin-like in its preference for arginyl as compared to lysyl chloromethyl ketones as well as by its inhibition by benzamidine and p-aminobenzamidine. However, the substrate specificity of the activator is distinguished from alpha-thrombin in that it does not clot fibrinogen and does not react with antithrombin III or hirudin.(ABSTRACT TRUNCATED AT 250 WORDS)

Crotalid Venoms↗
PubMed1985

Thrombin-induced conformational changes of human alpha 2-macroglobulin: evidence for two functional domains.

The interaction of thrombin with alpha 2-macroglobulin (alpha 2M) was characterized by monitoring conformational changes and measuring the increase of free sulfhydryl groups during the reaction. Under experimental conditions where [thrombin] greater than [alpha 2M], the conformational change, measured by increases in the fluorescence of 6-(p-toluidino)-2-naphthalenesulfonate, and thiol group appearance displayed biphasic kinetics. The initial rapid phase results in the formation of a stable complex, the appearance of two sulfhydryl groups, the cleavage of approximately half of the Mr 180 000 subunits, and a conformational change that is not as extensive as that which occurs with trypsin. The slower phase is associated with the appearance of two additional sulfhydryl groups, increased cleavage of the Mr 180 000 subunit, and additional conformational changes. The available evidence suggests that the slow phase results from hydrolysis of the Mr 180 000 subunit(s) due to proteolysis of the alpha 2M-thrombin complex by free thrombin. Experiments with 125I-thrombin document the binding of 1 mol of thrombin/mol of alpha 2M that is not dissociated upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the complex. At higher ratios of thrombin to alpha 2M, a second mole of thrombin will reversibly associate with the 1:1 alpha 2M-thrombin complex. Under conditions where [thrombin] less than [alpha 2M], biphasic kinetics were not observed, and the conformational change, sulfhydryl appearance, and hydrolysis of the Mr 180 000 subunit were found to follow second-order kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Dithionitrobenzoic Acid↗
PubMed1985

Autogenous regulation of transcription termination factor Rho.

We present evidence that the transcription termination factor Rho is autogenously regulated in Escherichia coli. The steady-state level of Rho is increased approximately tenfold in rho mutant cells. In the rho+ revertants, the content of Rho is similar to the wild-type level. A rho-/rho+ merodiploid produces equimolar amounts of the mutant and the wild-type Rho polypeptides, both at a reduced level compared to the mutant. The steady-state level of rho messenger RNA is also increased in a rho mutant. A rho-galK transcriptional fusion produces at least tenfold more galactokinase in a rho- strain than in a rho+ strain. In vitro, in a coupled transcription-translation system, the synthesis of Rho protein is specifically inhibited by wild-type Rho but not by Rho15 mutant protein. Anti-Rho antibody specifically stimulates Rho synthesis in the rho+ extract but not in a rho- extract. We suggest that the autogenous regulation of Rho involves premature transcription termination within the rho gene. Regulation of Rho level may provide the cell a mechanism to modulate the expression of genes which are separated from their promoters by Rho-dependent termination signals.

Adenosine Triphosphatases↗
PubMed1984

Kinetics of the conformational alterations associated with nucleophilic modification of alpha 2-macroglobulin.

The effect of nucleophilic modification of alpha 2-macroglobulin (alpha 2M) with methylamine on the kinetics of sulfhydryl exposure was investigated. The generated sulfhydryl groups were detected with 4,4'-dithiodipyridine. The bimolecular rate constant for sulfhydryl exposure was determined to be 11.6 +/- 0.8 M-1 s-1 at 30 degrees C and pH 8.0. Treatment of alpha 2-macroglobulin with methylamine or proteases, such as plasmin and trypsin, results in a substantial increase in the fluorescence of 6-(p-toluidino)-2-naphthalenesulfonic acid. This probe was used to monitor the kinetics of the conformational change occurring in alpha 2-macroglobulin upon treatment with methylamine. It was found that the conformational change did not occur simultaneously with the cleavage of the thiol ester bonds by the nucleophile but, rather, the conformational alterations occurred following a lag phase. The data are consistent with a mechanism requiring the random cleavage of two thiol ester bonds of a dimeric unit in the molecule prior to the unimolecular process representing the conformational change. According to this model, the two dimeric units present in alpha 2M act as independent entities. On the basis of the best fit with the model, the bimolecular rate constant, for hydrolysis of the thiol ester bonds, was determined to be 11.9 +/- 0.7 M-1 s-1, while the rate constant for the conformational change was (9.7 +/- 2.0) X 10(-3) s-1. The measured rate of conformational change is rate limited by thiol ester cleavage at lower methylamine concentrations. The conformational change, measured with this fluorescence probe, approximately parallels the loss of trypsin binding activity of alpha 2-macroglobulin, measured by resistance of the bound trypsin to soybean trypsin inhibitor. A much slower loss of plasmin binding activity was observed than was found for trypsin, suggesting that the structural requirements on alpha 2M for the interaction with plasmin are disrupted much more slowly than the structural requirements for trypsin binding upon methylamine treatment of the molecule.

Fluorescent Dyes↗
PubMed1982

Probable involvement of a glycoconjugate in IMR-32 DNA synthesis: decrease of DNA polymerase alpha 2 activity after tunicamycin treatment.

Multiple forms of DNA polymerase alpha activity (alpha 1, alpha 2, and alpha 3) from human neuroblastoma IMR-32 cells untreated or treated with tunicamycin (3 microgram/ml) were separated by DEAE-cellulose column chromatography. Loss of 40--60% of DNA polymerase alpha 2 activity was observed in tunicamycin-treated cells. Ricin 1B, a subunit of intact ricin (Mr, 64,000), was found to be a specific inhibitor of DNA polymerase alpha 2 isolated from control IMR-32 cells. However, DNA polymerase alpha 2 isolated from tunicamycin-treated cells was insensitive to ricin 1B. Heat treatment studies at 50 degrees C showed two completely different inactivation profiles for the DNA polymerase alpha 2 enzymes isolated from the tunicamycin-treated and untreated cells. A probable involvement of a beta-linked galactose-containing carbohydrate chain in the catalytic subunit of DNA polymerase alpha 2 is suggested.

Cells, Cultured↗