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Biomedical subjects

S K Biswas

Publications and source records attributed to S K Biswas.

At least 19 recordsLinked to original sources
PubMed1996

Influenza virus polymerase basic protein 1 interacts with influenza virus polymerase basic protein 2 at multiple sites.

Three polymerase proteins of influenza type A virus interact with each other to form the active polymerase complex. Polymerase basic protein 1 (PB1) can interact with PB2 in the presence or absence of polymerase acidic protein. In this study, we investigated the domains of PB1 involved in complex formation with PB2 in vivo, using coexpression and coimmunoprecipitation of the PB1-PB2 complex with monospecific antibodies. Results show that PB1 possesses at least two regions which can interact independently and form stable complexes with PB2. Both of these regions are located at the NH2 terminus of PB1; the COOH-terminal half of PB1 is not involved in interacting with PB2. Deletion analysis further demonstrated that the interacting regions of PB1 encompass amino acids (aa) 48 to 145 and aa 251 to 321. Linker insertions throughout the PB1 sequences did not affect complex formation with PB2. Deletion and linker-insertion mutants of PB1 were tested for polymerase activity in vivo. For this analysis, we developed a simplified assay for viral polymerase activity that uses a reporter chloramphenicol acetyltransferase gene containing the 5' and 3' ends of influenza viral promoter and nontranslating regions (minus sense) of the NS gene joined to a hepatitis delta virus ribozyme at its 3' end. This assay demonstrated that all deletion mutants of PB1 exhibited either background or greatly reduced polymerase activity irrespective of the ability to interact with PB2 and that all linker-insertion mutants except one at the extreme COOH end (L-746) of PB1 were also negative for viral polymerase activity. These results show that compared with complex formation of PB1 with PB2, the polymerase activity of PB1 was extremely sensitive to structural perturbation.

Binding Sites↗
PubMed1994

Mutational analysis of the conserved motifs of influenza A virus polymerase basic protein 1.

Influenza virus polymerase complex is a heterotrimer consisting of polymerase basic protein 1 (PB1), polymerase basic protein 2 (PB2), and polymerase acidic protein (PA). Of these, only PB1, which has been implicated in RNA chain elongation, possesses the four conserved motifs (motifs I, II, III, and IV) and the four invariant amino acids (one in each motif) found among all viral RNA-dependent RNA or RNA-dependent DNA polymerases. We have modified an assay system developed by Huang et al. (T.-J. Huang, P. Palese, and M. Krystal, J. Virol. 64:5669-5673, 1990) to reconstitute the functional polymerase activity in vivo. Using this assay, we have examined the requirement of each of these motifs of PB1 in polymerase activity. We find that each of these invariant amino acids is critical for PB1 activity and that mutation in any one of these residues renders the protein nonfunctional. We also find that in motif III, which contains the SSDD sequence, the signature sequence of influenza virus RNA polymerase, SDD is essentially invariant and cannot accommodate sequences found in other RNA viral polymerases. However, conserved changes in the flanking sequences of SDD can be partially tolerated. These results provide the experimental evidence that influenza virus PB1 possesses a similar polymerase module as has been proposed for other RNA viruses and that the core SDD sequence of influenza virus PB1 represents a sequence variant of the GDN in negative-stranded nonsegmented RNA viruses, GDD in positive-stranded RNA virus and double-stranded RNA viruses, or MDD in retroviruses.

Amino Acid Sequence↗
PubMed1993

Status of nitric oxide free radicals in diabetic neutrophils: effect of diabetic serum factor on the generation of these species in normal neutrophils and their relation to lysosomal degranulation.

Normal polymorphonuclear leukocytes (PMNL) in contrast to diabetic PMNL, generated significant amounts of .NO and NO2 when challenged with opsonised zymosan. Diabetic neutrophils, on the other hand, responded either weakly or insignificantly to the same stimulants. However, in resting state the levels of .NO and NO2 were higher in diabetic as compared to normal PMNL. Diabetic serum factor (DSF) provoked a significant generation of .NO and NO2 in normal PMNL, a phenomenon found parallel to the enhancement in cytosolic cathepsin D activity in normal cells on insult with DSF.

Biological Factors↗
PubMed1993

Effect of tri-ortho-cresyl phosphate on hen nervous system.

Correlation of tri-ortho-cresyl phosphate (TOCP) toxicity with clinical symptoms and inhibition patterns of neurotoxic esterase (NTE) in different regions of the central nervous system was studied in hens. The total content of NTE in spinal cord and peripheral nerves was relatively much lower than that of the brain, about 29 and 4.8 per cent respectively. Brain and spinal cord NTE was inhibited to 75 and 67 per cent respectively on day 1 post-TOCP treatment, and 91 and 84 per cent respectively on day 2, while the activity of the enzyme in peripheral nerve was inhibited to 92 per cent on day 1. However, the clinical manifestations of paralysis appeared after 7-8 days of TOCP treatment. It can be concluded that the presence of NTE in very low quantities in the peripheral nerves and its almost complete inhibition as compared to that of brain and spinal cord, could be of great significance in the development of neurotoxicity.

Animals↗
PubMed1992

An unusual case of heteropagus twinning.

A 3-day-old boy baby presented with a cystic umbilical swelling covered mostly by skin and partly by amnion. On the surface, an early embryo-like structure was attached (facial features and limb buds). The deeper aspect of it was composed of large cystic and tubular structures and solid organs resembling liver and spleen. It was labeled as acardiac amorphous parasitic twin, the first of its kind to be reported.

Hernia, Umbilical↗
PubMed1992

A 14-kilodalton inner membrane protein of Vibrio cholerae biotype e1 tor confers resistance to group IV choleraphage infection to classical vibrios.

Choleraphage phi 149 differentiates the two biotypes, classical and el tor, of Vibrio cholerae. This phage cannot replicate in V. cholerae biotype el tor cells because the concatemeric DNA intermediates produced are unstable and cannot be chased to mature phage DNA. A V. cholerae biotype el tor gene coding for a 14,000-Da inner membrane protein which destabilizes the concatemeric DNA intermediates by hindering their binding to the cell membrane has been identified. Presumably, a 22,000-Da V. cholerae biotype el tor protein might also have a role in conferring phage phi 149 resistance to cells belonging to the biotype el tor. A nucleotide sequence homologous to the 1.2-kb V. cholerae biotype el tor DNA coding for both the 14,000- and 22,000-Da proteins is present in all strains of classical vibrios but is not transcribed. The nucleotide sequence of the gene coding for the 14,000-Da protein has been determined.

Amino Acid Sequence↗
PubMed1990

Urine level of trace elements in some adults in Bangladesh under a workplace environment.

The urine level of trace elements has been investigated in some normal adults under different workplace environments in Bangladesh. The samples were collected from 58 subjects, randomly selected from about 500 adults working in 10 different workshops and factories located in Dhaka city. Samples were analyzed by the external beam PIXE method. Proton beams of 2.5 MeV energy and 20 nA intensity were used for sample irradiations. For 40 microC irradiations, the concentration of 14 elements in total (K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Br, Rb, Sr and Mo) in different groups were measured by comparison with a calibration curve obtained from the NBS Orchard Leaf standard (SRM 1571). The results from different workplaces are reported in terms of amount of excretion per unit volume of the sample collected. They, however, do not reflect the total daily excretion level of different subject groups.

Adult↗
PubMed1989

Subtotal cystectomy and antirefluxing hepaticoduodenostomy for choledochus cyst in children.

Total cystectomy with Roux-en-Y hepaticojejunostomy for choledochus cyst often causes malabsorption and other problems as a result of jejunal biliary diversion bypassing the duodenum. Restoration of near normal anatomy can only return the normal physiological harmony and assure normality. A simple antirefluxing hepaticoduodenostomy has proved successful.

Anastomosis, Roux-en-Y↗
PubMed1989

Abortive replication of choleraphage phi 149 in Vibrio cholerae biotype el tor.

Choleraphage phi 149 adsorbed irreversibly to Vibrio cholerae biotype el tor cells, and 50% of the injected phage DNA bound to the cell membrane. Although no infectious centers were produced at any time during infection, the host macromolecular syntheses were shut off and the host DNA underwent chloramphenicol-inhibitable degradation. Synthesis of monomeric phage DNA continued similar to that observed in the permissive host. However, the concatemeric DNA intermediates produced were unstable and could not be chased to mature phage DNA. Pulse-labeling of UV-irradiated infected cells at different times during infection allowed identification of phage-specific proteins made in this nonpermissive host. Although most of the early proteins were made, only some of the late proteins were transiently synthesized.

Bacteriophages↗
PubMed1989

Cultivation of Mycobacterium leprae in artificial culture medium.

A novel procedure in the cultivation of M. leprae in combined Dubos-Lowenstein-Jenson medium after addition of thyroxine sodium is being reported. This has been found to be successful as the organisms, after multiplying vigorously in the thyroxine containing Dubos medium, have produced a visible colony on the surface of Lowenstein-Jensen medium during 8-16 wks of incubation at 37 degrees C. The enhanced growth of this recalcitrant organism is due to stimulating effect of thyroxine as well as supply of ready-made basic nutrients in the synthetic Dubos medium. Intradermal inoculation of the bacterial suspension from the subculture into the foot pad of cortisone treated mouse revealed an early appearance of specific histological lesion of leprosy with infiltration of nerve fibres by lepra cells. The methodology, described here for in-vitro cultivation, may open out a new era in the preparation of purified vaccine, the study of in-vitro drug sensitivity, and as such ensure rapid eradication of leprosy.

Bacteriological Techniques↗
PubMed1988

Selective devascularisation of stomach and lienopulmopexy for prevention of bleedings in portal hypertension in children.

Dissatisfied with different operative procedures for prevention of recurrent bleedings in childhood portal hypertension, many surgeons nowadays treat their patients conservatively during episodic attacks and advocate one of the shunt procedures in adolescence when the splenic vein becomes sufficiently widened (more than 1 cm). Even then mortality cannot be avoided in some bad risk patients especially those living in remote villages lacking facilities for blood transfusion and high speed transport service. In this situation thoracic transposition of spleen and lienopulmopexy was advocated by Nylander and Turumen, Auvert, M. Bettex and others. We prefer a further simpler procedure and perform selective devascularisation of stomach and lienopulmopexy. It allows rapid development of collaterals between splenic pulps on the portal side and subpleural venous plexus on the systemic side to achieve effective gastric devascularisation to prevent further bleeding without hindering the existing portal flow through the liver to avoid the possible occurrence of encephalopathy. Of 21 operated cases one died on the 5th postoperative day and the remaining 20 are doing well. 1/2-5 1/2 years' follow-up revealed negligible morbidity and no recurrence of bleeding in any of them. Both procedures work on the same principle.

Child↗
PubMed1984

Multielement proton-induced X-ray emission analysis of Bangladeshi tobacco.

The concentration of 12 different elements in cigarette tobacco of different brands, commercially made in Bangladesh, was determined using the proton particle-induced x-ray emission (proton PIXE) method. In all the present experiments, proton beams of 2.0 MeV (on the target in air) and about 30 nA current were used for characteristic x-ray excitation. The concentration of the elements (K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb and Sr) was determined by comparison with a calibration obtained from the NBS orchard leaf standard, SRM 1571. The results have been compared with available data on some foreign brands of tobacco and the probable reasons for the difference in the contents of some of the elements found in the Bangladeshi brands are discussed.

Bangladesh↗