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K Islam

Publications and source records attributed to K Islam.

At least 55 records · Page 3Linked to original sources
PubMed1995

Monochromosome transfers to Syrian hamster BHK cells via microcell fusion provide functional evidence for suppressor genes on human chromosome 9 both for anchorage independence and for tumorigenicity.

We previously identified an anchorage independence-suppressor gene, SAII, on rat chromosome (RNO) 5. RNO5 is homologous to human chromosomes (HSA) 1 and 9. In order to find the human homolog of the SAII gene, we transferred HSA1 and HSA9 to an anchorage-independent and tumorigenic Syrian hamster BHK 191-5C cell line by microcell fusion. For HSA9, we used a t(X;9)-derivative chromosome to force the retention of this chromosome in hybrids by hypoxanthine-aminopterin-thymidine (HAT) selection. To study the possible effect of the X portion of the der(9)t(X;9), we also transferred a normal X to 191-5C cells. For HSA1, a neo-tagged chromosome was introduced. Following the transfer of der(9)t(X;9) to 191-5C cells, the hybrid cells became anchorage dependent and nontumorigenic, and, upon the loss of this chromosome, the cells regained their tumorigenic and anchorage-independent phenotypes. The transfer of HSAX or HSA1, on the other hand, affected neither of these phenotypes. These results provide functional proof of suppressor genes on HSA9 involving both anchorage independence and tumorigenicity. In addition, our data suggest the presence of another gene on HSA9 that causes a negative growth effect and whose phenotypic expression, contrary to the suppressor genes, is dosage dependent.

Animals↗
PubMed1995

Effect of amino acid substitutions on calmodulin binding and cytolytic properties of the LLP-1 peptide segment of human immunodeficiency virus type 1 transmembrane protein.

Previous studies have identified two highly basic amphipathic helical regions in the human immunodeficiency virus type 1 transmembrane protein that, in vitro, display both cytolytic and calmodulin-binding and -inhibitory properties that could contribute to cellular dysfunctions and cytopathogenesis during a persistent viral infection. In the current study, the structural specificity of the cytolytic and calmodulin-binding activities of the human immunodeficiency virus type 1 lentivirus lytic peptide (LLP-1) are examined with synthetic peptide homologs and analogs. The results of these studies demonstrate that even minor changes in LLP-1 amino acid content can markedly affect these properties, suggesting that sequence variation in these highly conserved LLP sequences may correlate with alterations in viral cytopathic properties.

Amino Acid Sequence↗
PubMed1995

Comparison between thymidylate synthase B of Bacillus subtilis ATCC6633 and 168.

Bacillus subtilis 168 possesses two thymidylate synthase genes: thyA and thyB, encoding for a thermolabile and a thermostable enzyme respectively. B. subtilis ATCC6633 also possesses two thy genes, both producing thermostable enzymes. A comparison of the thymidylate synthase B amino acid sequences from the two strains shows, among others, a Pro to Ala mutation which may affect the dUMP binding site. The apparent Km and Vmax values for dUMP and tetrahydrofolate were determined at a permissive temperature for both enzymes. The kinetic data showed a significant difference in the Km, but not in the Vmax, for dUMP between the two enzymes. The Km and Vmax for tetrahydrofolate were very similar.

Alanine↗
PubMed1994

Purified native microtubule associated protein MAP1A: kinetics of microtubule assembly and MAP1A/tubulin stoichiometry.

In a recent study, we have shown that sulfonate buffers affect microtubule assembly and alter microtubule protein composition (Pedrotti et al., 1993). In particular, we noted that PIPES buffer leads to removal of MAP1 from the microtubule surface without affecting the association of MAP2 with microtubules. This observation has been exploited to develop a simple purification procedure for MAP1A using twice-cycled microtubule protein prepared from whole bovine brain. A single chromatographic step on an ion-exchange column results in > 90% pure MAP1A. Using purified MAP1A, we now show that MAP1A (a) binds in a dose-dependent manner to unpolymerized tubulin and assembled microtubules, (b) binds 13-15 mol of tubulin dimers in assembled microtubules, (c) promotes both nucleation and elongation of tubulin, and (d) promotes incorporation of tubulin dimers at low GTP concentrations and of tubulin dimers and oligomers at high GTP concentrations. MAP1A lowers the critical concentration for assembly, and MAP1A-promoted incorporation of dimers has an association rate constant (K+1) of 39.3 x 10(6) M-1s-1 and a dissociation rate constant (K-1) of 15 s-1; both constants are about 2-3-fold higher compared with MAP2.

Animals↗
PubMed1994

Interactions of microtubule-associated protein MAP2 with unpolymerized and polymerized tubulin and actin using a 96-well microtiter plate solid-phase immunoassay.

A solid-phase immunoassay is used to study the protein-protein interactions between microtubule-associated protein MAP2 and the cytoskeletal proteins tubulin and actin. The assay can be performed on 96-well microtiter plates and can be used to study the interactions with both subunit proteins and their respective polymers, microtubules and microfilaments. The microtiter format allows a large number of samples to be processed, and a number of conditions can be varied. In this solid-phase immunoassay MAP2 bound to microtubules/microfilaments and tubulin dimers/G-actin in a concentration-dependent manner. However, the bound MAP2 was not dissociated from the filaments even at high NaCl concentrations, while simultaneous addition of NaCl diminished MAP2 binding to these proteins. MgCl2 was 1 order of magnitude more efficient in decreasing MAP2 binding compared with NaCl, suggesting that MAP2 may act by "screening" the electrostatic repulsion between tubulin dimers. The role of MAP2 in cross-linking microfilaments and microtubules was also examined. Microtubule/tubulin-bound MAP2 showed a diminished ability to bind to both microfilaments and G-actin, while microfilament/G-actin-bound MAP2 was able to bind efficiently to both microtubules and tubulin dimers.(ABSTRACT TRUNCATED AT 250 WORDS)

Actin Cytoskeleton↗
PubMed1994

Microtubule associated protein MAP1A is an actin-binding and crosslinking protein.

High molecular weight microtubule-associated proteins MAP1A and MAP2 form thin projections from microtubule surfaces and have been implicated in crosslinking microtubules and other cytoskeletal components. We have purified native MAP1A from bovine brain and have studied its interaction with G- and F-actin. Using a solid-phase immunoassay we show that MAP1A binds in a dose-dependent manner to both G-actin and F-actin. Addition of MAP1A to F-actin causes gelation of F-actin and SDS-PAGE analysis shows that MAP1A co-sediments with the gelled network, under conditions where F-actin alone does not pellet. The low apparent viscosity of F-actin is markedly increased in the presence of MAP1A, suggesting that MAP1A can crosslink F-actin. Co-incubation experiments indicate that MAP1A and MAP2 may bind to common or overlapping sites on the actin molecule. The widespread distribution of MAP1A and its interaction with microtubules, actin, and intermediate filaments suggests that it may constitute an important determinant of neuronal and non-neuronal cellular morphology.

Actins↗
PubMed1994

Purification procedure for bacterial translational initiation factors IF2 and IF3.

In bacteria the initiation of protein synthesis is a complex phenomenon in which specific proteins, termed initiation factors (IFs) IF1, IF2, and IF3, are involved. Notwithstanding the progress made in understanding their functions, the precise molecular mechanisms of action of these factors remain somewhat obscure. One reason for this lack of knowledge is the difficulty involved in purifying sufficient quantities of these proteins. We have developed a new procedure for purification of IFs from recombinant Escherichia coli strains producing high levels of E. coli IF3 and Bacillus stearothermophilus IF2. This new procedure is quicker than previous methods, easily scaled up to large volumes, and can be used, with only minor modifications, for different IFs. This new purification method consists essentially of one chromatographic (FPLC) separation on an ion-exchange resin (S-Sepharose fast-flow or Mono-S HR). Using this procedure we have been able to obtain chromatographically pure and biologically active preparations of both IF2 and IF3.

Bacterial Proteins↗
PubMed1994

D-cycloserine uses an active transport mechanism in the human intestinal cell line Caco 2.

In a previous study we have shown that cultured epithelial cell lines can be used to measure the transepithelial passage of antimicrobial agents across the intestine and to obtain information on the mechanisms of transport utilized and predict the bioavailability of the antimicrobial agents after oral administration. In particular, among the drugs investigated, D-cycloserine had been shown to be transported in a polarized manner only in the intestinal cells. In the present work, further characterization of the transport of D-cycloserine in the human intestinal cell line Caco 2 has shown that this occurs in the apical-to-basolateral direction by an active mechanism which is energy dependent but only partially sodium dependent. Competition studies have also indicated that the transport of D-cycloserine occurs via a carrier for imino acids, amino acids with aliphatic side chains (L-Ala, D-Ala, and beta Ala), and L-Trp, L-Tyr, L-Cys, and alpha-amino isobutyric acid. This system may correspond to a proton-dependent system for L-proline and beta-alanine recently described for Caco 2 cells. In contrast with the cephalosporins, which are taken up by the Caco 2 cells via a dipeptide carrier, D-cycloserine transport cannot be inhibited by either cephalexin (a member of the class of cephalosporins) or dipeptides.

Biological Transport, Active↗
PubMed1994

Assignment of TK1 encoding thymidine kinase to Syrian hamster chromosome 9 by microcell-mediated chromosome transfer.

We report here the assignment of TK1, the gene for thymidine kinase to Syrian hamster (Mesocricetus auratus) chromosome 9 (MAU9) by complementation mapping. Syrian hamster chromosomes derived from a wild type (TK+) subline of BHK cells were introduced via microcell-mediated chromosome transfer into B82 mouse cells deficient in thymidine kinase (TK-), a defect that prevents their growth in HAT culture media. Hybrid clones were selected in HAT media. Chromosome analyses of the microcell hybrids showed that the thymidine kinase deficiency of B82 cells was corrected by MAU9. Therefore, we assigned TK1 to MAU9. Previously, TK1 was assigned to mouse chromosome 11 (MMU11), rat chromosome 10 (RNO10), Chinese hamster chromosome 7 (CGR7), and human chromosome 17 (HSA17). The striking banding homology of MAU9 with RNO10, MMU11, CGR7 and HSA17 provides additional support for the assignment of TK1 to MAU9. To our knowledge, this is the first report of gene assignment to a specific Syrian hamster chromosome using the somatic cell hybridization technique.

Animals↗
PubMed1993

Peptide aldehydes as inhibitors of HIV protease.

We have recently shown that alpha-MAPI, a peptidic aldehyde of microbial origin, inhibits the HIV protease with a potency comparable to pepstatin, having, differently from pepstatin, no activity on other aspartic proteases. In this study different peptide derivatives containing a C-terminal aldehyde have been tested to assess the potential of this function for the inhibition of HIV protease. The results of our analysis correspond with the recently published subsite preferences of the viral enzyme, indicating that aldehydes bind to the active site of the HIV protease. Our data suggest that peptide aldehydes can act in their hydrated forms as transition state analogues with the most potent inhibitor having an IC50 of 0.9 microM.

Aldehydes↗
PubMed1993

Sulphonate buffers affect the recovery of microtubule-associated proteins MAP1 and MAP2: evidence that MAP1A promotes microtubule assembly.

The influence of two commonly used sulphonate buffers, PIPES and MES, on the in vitro assembly of bovine brain microtubule protein was examined. Microtubule assembly was monitored by turbimetry and, after centrifugation, the polymerised protein was analysed by SDS-PAGE and western blotting. Assembly in MES when compared with PIPES resulted in a higher recovery of microtubule proteins at both pH 6.4 and pH 6.9 and in an altered protein composition. The buffer pH affected the total amount of protein polymerised but did not significantly affect the protein composition. At both pH conditions the recovery of HMW-MAPs was markedly increased in MES buffer and this increase was mostly due to an increase in the amount of MAP1.

Alkanesulfonic Acids↗
PubMed1993

The effects of doxorubicin on embryonic spinal motoneurons cultured in vitro: cytoskeletal response.

The interaction of doxorubicin with tubulin in spinal motoneuronal cells cultured in vitro has been examined by laser scan microscopy with an immunocytological double staining technique, and by biochemical analysis. Results obtained by laser scan microscopy indicate that doxorubicin (2 x 10(-8) M) was able to induce fragmentation or disappearance of microtubules in motoneuronal cells. Motoneurons were identified by their positivity to anti-CAT antibody. This observation was then studied by biochemical analysis on purified calf brain tubulin. Even treatment with a high dose of doxorubicin (1.2 x 10(-5) M) does not impair tubulin polymerization. The finding supports the possibility that doxorubicin interacts with MAPs or other polypeptides present in the cytomatrix that coassemble with tubulin and are necessary for microtubule formation.

Animals↗
PubMed1993

Plasma level of antioxidant nutrients (retinol and alphatocopherol) in cases with different grades of cervical carcinoma.

A study was conducted on 23 patients on various grades of cervical cancer, selected purposely from Dhaka Medical College Hospital. Vitamin A and E level of this histologically proved cases showed mean serum level of vitamin A was 0.41 +/- 0.19 and that vitamin E was 4.21 +/- 2.15, and these low level was constant in all Histopathological grading of cervical cancer. Contraceptive user and smoker had very low level of vitamin A and E. Majority (51%) of the cases, were from lower middle class and 49% were from lower class, seventy seven percent were illiterate, 97% were married before 18 years, 57% had more than 6 children, 71% did not use contraceptive. The availability of vitamin A rich food were within reach of lower income group, than the food source of vitamin E which are usually of animal origin. It is concluded that in cervical cancer had low level of antioxidant vitamins A and E. Further study is indicated for understanding detail antioxidant nutrients role in aetiopathology of cervical cancer in Bangladesh.

Adult↗
PubMed1993

Risk factors for mortality in the Bangladesh cyclone of 1991.

Cyclones continue to pose a dangerous threat to the coastal populations of Bangladesh, despite improvements in disaster control procedures. After 138,000 persons died in the April 1991 cyclone, we carried out a rapid epidemiological assessment to determine factors associated with cyclone-related mortality and to identify prevention strategies. A nonrandom survey of 45 housing clusters comprising 1123 persons showed that mortality was greatest among under-10-year-olds (26%) and women older than 40 years (31%). Nearly 22% of persons who did not reach a concrete or brick structure died, whereas all persons who sought refuge in such structures survived. Future cyclone-associated mortality in Bangladesh could be prevented by more effective warnings leading to an earlier response, better access to designated cyclone shelters, and improved preparedness in high-risk communities. In particular, deaths among women and under-10-year-olds could be reduced by ensuring that they are given special attention by families, neighbours, local authorities, and especially those in charge of early warnings and emergency evacuation.

Adult↗
PubMed1992

Inhibition of bacterial protein synthesis by elongation-factor-Tu-binding antibiotics MDL 62,879 and efrotomycin.

MDL 62,879 (formerly GE 2270 A) is a novel antibiotic active against Gram-positive bacteria by inhibiting protein synthesis. MDL 62,879 is not active against Gram-negative bacteria, but inhibits cell-free protein synthesis in extracts from Escherichia coli, and shows a high binding affinity for its elongation factor Tu (EF-Tu). We prepared ribosomes and protein-synthesis elongation factors from three sources: E. coli, Bacillus subtilis, and a strain of B. subtilis selected for resistance to MDL 62,879 (strain G1674). Homologous and heterologous reconstituted systems were used to compare the effects of MDL 62,879 and of efrotomycin, an EF-Tu inhibitor of the kirromycin class, which is inactive against both B. subtilis and E. coli. We showed that in cell-free protein synthesis: (a) E. coli was sensitive to both MDL 62,879 and efrotomycin; (b) B. subtilis was sensitive to MDL 62,879, but not to efrotomycin; (c) B. subtilis G1674 was resistant to both antibiotics. In the E. coli system and in the system from wild-type B. subtilis, inhibition by MDL 62,879 was reversed upon addition of purified EF-Tu from B. subtilis G1674. This demonstrates that the antibiotic acts by inhibition of EF-Tu. In contrast, extracts from B. subtilis failed to restore activity in an efrotomycin-inhibited E. coli system. Dominance or resistance to MDL 62,879 and of sensitivity to efrotomycin in heterologous cell-free protein synthesis confirms that inhibition of EF-Tu by the two antibiotics is mediated by different mechanisms of action.

Anti-Bacterial Agents↗