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Biomedical subjects

A Das

Publications and source records attributed to A Das.

At least 397 records · Page 22Linked to original sources
PubMed1983

Lactate dehydrogenase level and protein pattern in the aqueous humour of patients with retinoblastoma.

The diagnostic significance of the lactate dehydrogenase (LDH) level and the protein pattern in the aqueous humour was evaluated in patients with retinoblastoma who presented with leukokoria. The mean LDH level for the 14 retinoblastoma patients was significantly greater than the mean for 6 patients with leukokoria but without retinoblastoma (p less than 0.05) and the mean for 10 patients (controls) with senile cataract (p less than 0.01). Cellulose acetate membrane electrophoresis was performed on the aqueous humour of six of the patients with retinoblastoma, four of the patients with other causes of leukokoria and eight of the control patients. It showed that the protein in the aqueous humour was predominantly albumin in the patients with retinoblastoma; the globulin in these cases was usually beta-globulin. The protein was mostly or completely albumin in the three patients with Coats' disease, and the protein pattern simulated that in normal serum (owing to hemorrhage) in the patient with retinal detachment. No protein was detectable in the aqueous humour of the control patients. Thus, determining either the LDH level or the protein pattern in the aqueous humour can serve as a useful adjunct to the clinical diagnosis of retinoblastoma.

Albumins↗
PubMed1982

Regulation of tryptophan operon expression by attenuation in cell-free extracts of Escherichia coli.

Expression of the tryptophan (trp) operon of Escherichia coli was shown to be regulated by attenuation in an in vitro DNA-dependent protein-synthesizing system. In extracts prepared from a temperature-sensitive tryptophanyl-tRNA synthetase mutant, plasmid-directed trpE enzyme synthesis was inhibited 2- to 3-fold by addition of purified wild type tryptophanyl-tRNA synthetase. When the extract used from a strain bearing a trpTts mutation that reduces charging of tRNATrp in vivo, a 2- to 3-fold increase in trpE enzyme synthesis was observed when an excess of uncharged wild type tRNATrp was added. Analysis of attenuation by measurement of trp mRNA synthesis was facilitated by constructing a plasmid (pAD1) containing the rpoC transcription terminator inserted early in trpE. Transcription proceeding past the trp attenuator of this plasmid terminates at this new terminator sequence and results in the production of a approximately 400-nucleotide long read-through transcript. Using this plasmid and extracts prepared from the tryptophanyl-tRNA synthetase mutant, a 4- to 8-fold decrease in relative read-through transcription was observed in response to exogenously added wild type tryptophanyl-tRNA synthase. Kinetic analyses of trp mRNA synthesis and studies using plasmid template DNAs bearing trp attenuator mutations indicate that translation of the leader peptide coding region of the transcript regulates transcription termination at the trp attenuator.

Cell-Free System↗
PubMed1982

Isolation and characterization of goat submaxillary-mucin.

Mucin from the submaxillary glands of goats was isolated by precipitation from an aqueous extract with a cationic detergent, followed by dissolution in CaCl2 solution, and fractionation on a DEAE-cellulose column, Five homogeneous, mucin fractions were isolated by NaCl-gradient elution of the column. One of the fractions was obtained in major yield (46%); it was homogeneous by paper electrophoresis, and contained carbohydrates (46.4%) and protein (48.9%). The sugars were fucose, galactose, glucose, mannose, 2-acetamido-2-deoxygalactose, 2-acetamido-2-deoxyglucose, and N-acetylneuraminic acid. The principal amino acids were alanine, glutamic acid, glycine, proline, serine, threonine, and valine. The proportions of these residues were determined.

Amino Acids↗
PubMed1982

Control of phage lambda development by stability and synthesis of cII protein: role of the viral cIII and host hflA, himA and himD genes.

The cII protein of bacteriophage lambda has a decisive role in the regulatory switch between the lysogenic and lytic pathways of viral development. Recent work has indicated that cII may be the primary control function providing for the initial partition between the two pathways, with other host and viral regulatory genes acting to determine the levels of cII in an infected cell. We have studied the synthesis and stability of cII protein with two experimental systems, phage infection and a cII-producing plasmid. We have found that the stability of cII is controlled by the host hflA and viral cIII genes; hflA protein facilitates degradation of cII, whereas cIII protects cII. The synthesis of cII appears to be under the positive control of the host himA and himD genes. We conclude that posttranscriptional regulation of cII by host and viral genes is critical for the choice of a developmental pathway.

Bacteriophage lambda↗
PubMed1981

Protein synthesis in rabbit reticulocytes. Purification and characterization of a double-stranded RNA-dependent protein synthesis inhibitor from reticulocyte lysates.

Reticulocyte lysates contain a latent form of eukaryotic peptide chain initiation factor 2 (eIF-2) kinase (dsI) which becomes activated in the presence of double-stranded RNA and ATP and inhibits protein synthesis. The latent form of dsI has been partially purified from reticulocyte ribosomal salt wash. The purified dsI has been activated by incubation in the presence of poly(rI).poly(rC) and [gamma 32P]ATP and the activated dsI has been further purified to near homogeneity. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, purified [32P]dsI shows an intensely staining 67,000-dalton polypeptide band which corresponds to a single 67,000-dalton radioactive band. During Sephadex (G-200) gel filtration, both the latent form of dsI and the activated dsI elute similarly with a peak corresponding to a molecular weight of 67,000. Purified dsI phosphorylates the 38,000-dalton subunit of eIF-2 and, under conditions of eIF-2 phosphorylation, dsI strongly inhibits AUG-dependent Met-tRNAf binding to 40 S ribosomes. Also, in partial reactions, eIF-2 alpha (P) formed by phosphorylation of eIF-2 using dsI and ATP, is not recognized by two eIF-2 ancillary factors, Co-eIF-2B and Co-eIF-2C. These results are similar to those reported previously for the heme-regulated eIF-2 kinase (Das, A., Ralston, R. O., Grace, M., Roy, R., Ghosh-Dastidar, P., Das H. K., Yaghmai, B., Palmieri, S., and Gupta, N. K. (1979) Proc. Natl. Acad. Sci. U. S. A. 76,5076-5079) and suggest that dsI, like the heme-regulated eIF-2 kinase phosphorylates eIF-2 and eIF-2 alpha (P) thus formed, in both cases, is not recognized by Co-eIF-2B and Co-eIF-2C, and is inactive in some step(s) of Met-tRNAf.40 S initiation complex formation.

Adenosine Triphosphate↗
PubMed1981

Protein synthesis in rabbit reticulocytes. Co-eIF-2A reverses mRNA inhibition of ternary complex (Met-tRNAf.eIF-2.GTP) formation by eIF-2.

mRNAs, at low concentrations, drastically inhibit ternary complex formation by eIF-2 (Met-tRNAf.eIF-2.GTP) and, when added to the preformed ternary complex, cause extensive dissociation of the complex. Co-eIF-2A stimulates (2- to 4-fold) Met-tRNAf binding to eIF-2 and, in the presence of excess Co-eIF-2A, the stimulated Met-tRNAf binding to eIF-2 is fully resistant to mRNAs. Other cofactors tested such as Co-eIF-2B and Co-eIF-2C do not reverse mRNA inhibition of ternary complex formation.

Animals↗
PubMed1980

Protein synthesis in rabbit reticulocytes. Preparation of homogeneous Met-tRNAf deacylase and studies of its role in protein synthesis.

Met-tRNAf deacylase from reticulocyte ribosomes has been purified to homogeneity. Upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the homogeneous preparation gives a single protein band corresponding to a molecular weight of approximately 67,000. Purified Met-tRNAf deacylase degrades free Met-tRNAf and also Met-tRNAf bound to 40 S ribosomes in the presence of AUG codon but does not degrade Met-tRNAf in the ternary complex, Met-tRNAf.eIF-2.GTP. Purified Met-tRNAf deacylase does not inhibit protein synthesis in reticulocyte lysates at any concentration tested indicating that Met-tRNAf deacylase is not a protein synthesis inhibitor. Antibodies against Met-tRNAf deacylase have been prepared by immunizing a chicken with homogeneous preparation of Met-tRNAf deacylase. Addition of anti-Met-tRNAf deacylase does not have any effect on protein synthesis in reticulocyte lysates indicating that Met-tRNAf deacylase is not required for protein synthesis.

Acyltransferases↗
PubMed1980

Protein synthesis in rabbit reticulocytes. A study of the mechanism of interreaction of fluorescently labeled co-eIF-2A with eIF-2 using fluorescence polarization.

5-Dimethylaminonaphthalene-1-sulfonyl (dansyl)-Co-eIF-2A was prepared using homogeneous Co-eIF-2A. Dansyl-Co-eIF-2A was as active as untreated Co-eIF-2A when assayed for stimulation of ternary complex formation and also for protection of the ternary complex from dissociation by aurintricarboxylic acid. The mechanism of interaction of dansyl-Co-eIF-2A with eIF-2 was studied by measuring changes in fluorescence polarization. These studies indicate that dansyl-Co-eIF-2A interacts specifically with the ternary complex and does not interact with free eIF-2 or with two other high molecular weight protein complexes, Co-eIF-2B and Co-eIF-2C. Mg2+ inhibits ternary complex formation by eIF-2 and Co-eIF-2C relieves this Mg2+ inhibition of ternary complex formation. In both cases, the changes in fluorescence polarization of dansyl-Co-eIF-2A correlate well with the extent of ternary complex formed.

Animals↗
PubMed1980

Protein synthesis in rabbit reticulocytes. Demonstration of the requirements for eIF-2 and Co-eIF-2A for peptide chain initiation using immune sera.

Antisera to eIF-2 and Co-eIF-2A have been prepared by immunizing two chickens separately with homogeneous preparations of either eIF-2 or Co-eIF-2A. Addition of anti-eIF-2 or anti-Co-eIF-2A to reticulocyte lysates strongly inhibits protein synthesis and, in each case, protein synthesis inhibition is reversed by the addition of the corresponding homogeneous factor. Protein synthesis inhibition by anti-Co-eIF-2A is not reversed by eIF-2 at any concentration tested indicating an absolute requirement for Co-eIF-2A in protein synthesis. Also, in partial peptide chain initiation reactions, the addition of anti-Co-eIF-2A inhibits Co-eIF-2A stimulation of ternary complex formation by eIF-2 and Co-eIF-2A protection of ternary complexes in the presence of aurintricarboxylic acid.

Animals↗