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Biomedical subjects

A Ahmad

Publications and source records attributed to A Ahmad.

At least 55 records · Page 3Linked to original sources
PubMed2001

Leucine zipper motif of chicken histone acetyltransferase-1 is essential for in vivo and in vitro interactions with the p48 subunit of chicken chromatin assembly factor-1.

We cloned cDNA encoding chicken cytoplasmic histone acetyltransferase-1, chHAT-1, comprising 408 amino acids including a putative initiation Met. It exhibits 80.4% identity to the human homolog and possesses a typical leucine zipper motif. The glutathione S:-transferase (GST) pull-down assay, involving truncated and missense mutants of the chicken chromatin assembly factor-1 (chCAF-1)p48, revealed not only that a region (comprising amino acids 376-405 of chCAF-1p48 and containing the seventh WD dipeptide motif) binds to chHAT-1 in vitro, but also that mutation of the motif has no influence on the in vitro interaction. The GST pull-down assay, involving truncated and missense chHAT-1 mutants, established that a region, comprising amino acids 380-408 of chHAT-1 and containing the leucine zipper motif, is required for its in vitro interaction with chCAF-1p48. In addition, mutation of each of four Leu residues in the leucine zipper motif prevents the in vitro interaction. The yeast two-hybrid assay revealed that all four Leu residues within the leucine zipper motif of chHAT-1 are necessary for its in vivo interaction with chCAF-1p48. These results indicate not only that the proper leucine zipper motif of chHAT-1 is essential for its interaction with chCAF-1p48, but also that the propeller structure of chCAF-1p48 expected to act as a platform for protein-protein interactions may not be necessary for this interaction of chHAT-1.

Acetyltransferases↗
PubMed2001

Genetic diversity of Ostreopsis ovata (Dinophyceae) from Malaysia.

The genus Ostreopsis is an important component of benthic and epiphytic dinoflagellate assemblages in coral reefs and seaweed beds of Malaysia. Members of the species may produce toxins that contribute to ciguatera fish poisoning. In this study, two species have been isolated and cultured, Ostreopsis ovata and Ostreopsis lenticularis. Analyses of the 5.8S subunit and internal transcribed spacer regions ITS1 and ITS2 of the ribosomal RNA gene sequences of these two species showed that they are separate species, consistent with morphological designations. The nucleotide sequences of the 5.8S subunit and ITS1 and ITS2 regions of the rRNA gene were also used to evaluate the interpopulation and intrapopulation genetic diversity of O. ovata found in Malaysian waters. Results showed a low level of sequence divergence within populations. At the interpopulation level, the rRNA gene sequence distinguished two groups of genetically distinct strains, representative of a Malacca Straits group (isolates from Port Dickson) and a South China Sea group (isolates from Pulau Redang and Kota Kinabalu). Part of the sequences in the ITS regions may be useful in the design of oligonucleotide probes specific for each group. Results from this study show that the ITS regions can be used as genetic markers for taxonomic, biogeographic, and fine-scale population studies of this species.

Journal Article↗
PubMed2001

The infrequency of transmission of herpesviruses between humans and animals; postulation of an unrecognised protective host mechanism.

The infrequency of natural transmission of herpesviruses between humans and animals is surprising as there is extensive contact between humans and non-human species with unequivocal evidence that host cells from non-susceptible species will support replication of herpesviruses which do not seem to naturally infect that species. This review examines natural cross-infections between human and other species and suggests that, firstly, it is possible that humans and animals do become asymptomatically or symptomatically cross-infected from other species, but the infection is not diagnosed or not diagnosable by conventional methods; secondly, an as yet unidentified novel mechanism(s) may operate to prevent infection using chemical, electrical or as yet unidentified pathways and may even be 'switched on' by exposure to the virus.

Animals↗
PubMed2001

Studies on carboxymethyl cellulase produced by an alkalothermophilic actinomycete.

A novel alkalothermophilic actinomycete having optimum growth at pH 9 and 50 degrees C was isolated from self-heating compost from the Barabanki district of Uttar Pradesh, India. Based on its morphology, susceptibility of spores to heat and novobiocin, guaninecytosine content of chromosomal DNA and cell wall composition, the organism was classified under Thermomonospora. The alkalothermophilic actinomycete produced 23 IU/ml carboxymethyl cellulase (CMCase). The CMCase was purified by fractional ammonium sulphate precipitation followed by cellulose affinity chromatography and Sephacryl S-200 gel filtration. The CMCase had a molecular weight of 38 KD and pI of 4.1. The enzyme exhibited optimum activity at pH 5 and temperature 50 degrees C. The CMCase showed pH stability in the range 7-10. The enzyme retained 100% activity at 50 degrees C for 72 h and had half-lives of 7 and 3 h at 60 degrees C and 70 degrees C, respectively. The CMCase was stable in the presence of commercial detergents such as Ariel, Henko and Surf Excel, indicating its potential as an additive to laundry detergents.

Actinomycetales↗
PubMed2001

A novel thermostable xylanase from Thermomonospora sp.: influence of additives on thermostability.

An alkalothermophilic Thermomonospora sp. producing high levels of xylanase was isolated from self-heating compost. The culture produced 125 IU/ml of xylanase when grown in shake flasks at pH 9 and 50 degrees C for 96 h. The culture filtrate also contained cellulase (23 IU/ml), mannanase (1 IU/ml) and beta-xylosidase (0.1 IU/ml) activities. The xylanase was active at a broad range of pH (5-9) and temperature (40-90 degrees C). The optimum pH and temperature were 7 and 70 degrees C, respectively. The enzyme was stable in the pH range 5-8 and was thermostable with half-lives of 8 and 4 h at 60 degrees C and 70 degrees C, respectively, but only 9 min at 80 degrees C. The effects of a variety of compounds to enhance the stability of xylanase at 80 degrees C was studied. Addition of sorbitol, mannitol and glycerol increased the thermostability of xylanase in proportion to the number of hydroxyl groups per polyol molecule. Glycine also offered protection against thermoinactivation. Xylan, trehalose, gelatin and trehalose-gelatin mixture had marginal effect on the thermostability of xylanase at 80 degrees C.

Actinomycetales↗
PubMed2001

Evidence for a correlation between antibody-dependent cellular cytotoxicity-mediating anti-HIV-1 antibodies and prognostic predictors of HIV infection.

Using our gp120/41-expressing, NK cell activity-resistant CEM.NKR cell clones as targets in HIV-1-specific antibody-dependent cellular cytotoxicity (ADCC) assays, we demonstrate here that the serum titers of anti-HIV-1 ADCC antibodies bear a significant (P < 0.05) positive correlation with the peripheral blood CD4+ T cell counts and a negative one with the number of copies of HIV-1 RNA in the plasma of HIV-infected individuals. These findings underscore the importance of these antibodies as a protective immune parameter in these infections.

Antibody-Dependent Cell Cytotoxicity↗
PubMed2001

Correlation of spontaneous and induced premature atrial complexes initiating atrial fibrillation in humans: electrophysiologic parameters for guiding therapy.

INTRODUCTION: The low frequency of spontaneous premature atrial contractions (PACs) may be an impediment to mapping and ablation of atrial fibrillation (AF). It has been shown that PACs following external or internal cardioversion of AF can initiate AF. If this method could reproducibly induce PACs from the same location as spontaneous PACs, it would be clinically significant. High-resolution noncontact mapping can map a single beat, should help identify the sites of spontaneously occurring PACs and PACs induced following cardioversion of spontaneous or induced AF, and could help correlate the trigger sites for AF induction. METHODS AND RESULTS: Twelve patients (8 men and 4 women; mean age 49+/-10 years) with spontaneous PACs were included in the study. In all patients, AF was induced and subsequently cardioverted to assess and map isolated PACs or PACs that induced AF. Using the EnSite 3000 noncontact mapping system, mapping was performed of spontaneously occurring isolated PACs and PACs that induced AF and PACs (both with and without AF) that occurred on at least two different occasions following cardioversion. The locations of the spontaneous and the induced PACs were similar; 97% of induced PACs came from the same locations as those of spontaneous PACs (P = 0.5). Radiofrequency lesions guided by this mapping technique were delivered at 14 pulmonary vein sites. Following a single ablation attempt during a mean follow-up of 19+/-4 weeks, 42% of the patients were in sinus rhythm and drug-free, whereas an additional 24% of patients could be maintained in sinus rhythm on drugs that had failed before. CONCLUSION: There is a high degree of correlation between spontaneous and induced PACs as the trigger sites for AF initiation. Cardioversion of spontaneous or induced AF could be used as an electrophysiologic parameter for guiding therapy.

Adult↗
PubMed2001

Traumatic experiences and posttraumatic stress reactions in children and their parents from Kurdistan and Sweden.

This study was conducted to assess trauma scores and posttraumatic stress symptoms among Kurdistanian refugee children and their parents in Sweden and a comparable group of Swedish children and their parents. Comparative Kurdistanian and Swedish samples composed of 32 children each and their parents were interviewed by means of a specially devised trauma instrument (HUTQ-C), to identify traumatic events and to measure trauma scores, and with (PTSS-C) and (HTQ) to diagnose posttraumatic stress syndrome (PTSD) among children and adults, respectively. Although Kurdistanian parents reported considerably more traumatic events than Swedish parents, children in both samples showed more similarities than differences, both with regard to types and levels of traumatic events. Kurdistanian parents showed higher PTSD frequencies than Swedish parents. However, these differences proved to be significant with regard to both the mother's and the father's lifetime and current PTSD symptom scores. Kurdistanian parents have experienced more war traumas and differ with regard to trauma exposure and its consequences when compared with Swedish parents. Children from the two samples showed more similarities than differences with regard to reported trauma and PTSD-related symptoms. These results underline the significance of child-specific factors in trauma and PTSD.

Adolescent↗
PubMed2001

Novel bifunctional inhibitor of xylanase and aspartic protease: implications for inhibition of fungal growth.

A novel bifunctional inhibitor (ATBI) from an extremophilic Bacillus sp. exhibiting an activity against phytopathogenic fungi, including Alternaria, Aspergillus, Curvularia, Colletotricum, Fusarium, and Phomopsis species, and the saprophytic fungus Trichoderma sp. has been investigated. The 50% inhibitory concentrations of ATBI ranged from 0.30 to 5.9 microg/ml, whereas the MIC varied from 0.60 to 3.5 microg/ml for the fungal growth inhibition. The negative charge and the absence of periodic secondary structure in ATBI suggested an alternative mechanism for fungal growth inhibition. Rescue of fungal growth inhibition by the hydrolytic products of xylanase and aspartic protease indicated the involvement of these enzymes in cellular growth. The chemical modification of Asp or Glu or Lys residues of ATBI by 2,4,6-trinitrobenzenesulfonic acid and Woodward's reagent K, respectively, abolished its antifungal activity. In addition, ATBI also inhibited xylanase and aspartic protease competitively, with K(i) values 1.75 and 3.25 microM, respectively. Our discovery led us to envisage a paradigm shift in the concept of fungal growth inhibition for the role of antixylanolytic activity. Here we report for the first time a novel class of antifungal peptide, exhibiting bifunctional inhibitory activity.

Alternaria↗
PubMed2001

Family- and genus-level 16S rRNA-targeted oligonucleotide probes for ecological studies of methanotrophic bacteria.

Methanotrophic bacteria play a major role in the global carbon cycle, degrade xenobiotic pollutants, and have the potential for a variety of biotechnological applications. To facilitate ecological studies of these important organisms, we developed a suite of oligonucleotide probes for quantitative analysis of methanotroph-specific 16S rRNA from environmental samples. Two probes target methanotrophs in the family Methylocystaceae (type II methanotrophs) as a group. No oligonucleotide signatures that distinguish between the two genera in this family, Methylocystis and Methylosinus, were identified. Two other probes target, as a single group, a majority of the known methanotrophs belonging to the family Methylococcaceae (type I/X methanotrophs). The remaining probes target members of individual genera of the Methylococcaceae, including Methylobacter, Methylomonas, Methylomicrobium, Methylococcus, and Methylocaldum. One of the family-level probes also covers all methanotrophic endosymbionts of marine mollusks for which 16S rRNA sequences have been published. The two known species of the newly described genus Methylosarcina gen. nov. are covered by a probe that otherwise targets only members of the closely related genus Methylomicrobium. None of the probes covers strains of the newly proposed genera Methylocella and "Methylothermus," which are polyphyletic with respect to the recognized methanotrophic families. Empirically determined midpoint dissociation temperatures were 49 to 57 degrees C for all probes. In dot blot screening against RNA from positive- and negative-control strains, the probes were specific to their intended targets. The broad coverage and high degree of specificity of this new suite of probes will provide more detailed, quantitative information about the community structure of methanotrophs in environmental samples than was previously available.

Alphaproteobacteria↗
PubMed2001

Numerical simulation of the turbulent flow field distal to an aortic heart valve.

A numerical technique is described which simulates the turbulent flow through a aortic Jellyfish valve, for two volumetric flow rates of 15 and 26 l/min representing peak systole flow. The steady incompressible Navier-Stokes equations written in three-dimensional (3-D) format are solved iteratively using a computational fluid dynamics code (Bio-FL). The numerical results show that the flow at the edge of the membrane of the valve splits into two nearly symmetrical jets with similar phenomenological features. Moreover, the 3-D flow simulations indicate the existence of two vortices in the immediate vicinity of the valve ring. Although these vortices are attenuated rapidly downstream by diffusion, they can have an adverse effect on erythrocytes and active platelets. It is also shown that elevated shear stresses occur in the vicinity of the upstream surface of the open occluder. In general. the numerical predictions compare well with the experimental measurements made at various locations downstream of the valve. The locations and the values of maximum velocity and shear stress, as well as width and length of re-circulation regions, are correctly predicted.

Blood Flow Velocity↗
PubMed2001

Activated human platelets express Fas-L and induce apoptosis in Fas-positive tumor cells.

In addition to their role in hemostasis and thrombosis, platelets are important modulators of immune and inflammatory responses. We provide evidence here that human platelets contain abundant quantities of Fas-L, and upon activation, they express it on their surface as well as release it into medium. This surface-expressed Fas-L is biologically active and can induce apoptosis in Fas-positive human tumor cells. Therefore, activated platelets may represent an important player in Fas/Fas-L-mediated apoptosis.

Apoptosis↗
PubMed2001

Traumatic experiences and post-traumatic stress reactions in children from Kurdistan and Sweden.

UNLABELLED: This paper examines the types and scores of traumatic experiences, post-traumatic stress symptom and behavioural disorders among Kurdistanian refugee children in Sweden and a comparative Swedish group. The Harvard-Uppsala Trauma Questionnaire for Children (HUTQ-C), the Post-Traumatic Stress Disorder for Children (PTSS-C) and the Child Behaviour Checklist (CBCL) were administered in interview form to 32 children from each sample, controlled for age, gender and trauma levels. No significant differences were found between the 2 samples regarding types of traumatic events, frequencies of post-traumatic stress disorder, post-traumatic stress symptom scores or behavioural problem scores, except in 3 aspects: Kurdistanian children reported more war experience and being lost, while Swedish children presented higher frequencies of leisure-time accidents. CONCLUSION: This study supports the assumption that children differ from adults by showing more similarities than differences regarding traumatic experiences and post-traumatic stress reactions, after being exposed to an equivalent number of reported traumatic events. The refugee children's stay in Sweden can be considered as a healing factor.

Adolescent↗
PubMed2001

Modulation of expression of the MHC class I-binding natural killer cell receptors, and NK activity in relation to viral load in HIV-infected/AIDS patients.

The natural killer (NK) cells play an important role in viral infections via their spontaneous cytolytic activity against virus-infected cells as well as via secreting a variety of soluble mediators. The MHC class I-binding NK receptors of these cells have emerged as the most important regulators of the effector activities of cytolytic cells (both NK and CTL). We have studied the modulation of NK activity and the expression of NK receptors in HIV-infected/AIDS patients and report here that the NK activities of the patients with the lowest plasma HIV load were minimal and vice versa, suggesting a decrease in this activity following suppression of HIV replication. Interestingly, the NK activity correlated negatively with the peripheral blood CD4+ T-cell counts of these patients. Furthermore, these patients showed decreased percentages of CD56+ cells expressing NK receptors of the immunoglobulin superfamily, whereas the percentages of CD8+ cells expressing these receptors were increased. Moreover, the expression of C-type lectin-like NK receptor-associated invariant molecule CD94 was increased on CD8+ cells in these patients as compared with HIV-seronegative controls. These changes in the expression of NK receptors were also evident within groups of these patients having different viral loads. These results show, for the first time, decreased innate immunity and changes in the expression of NK receptors on cytolytic cells in relation to viral burden in HIV-infected/AIDS patient.

Adult↗
PubMed2001

Modelling viral and CD4 cellular population dynamics in HIV: approaches to evaluate intervention strategies.

Computational models, such as in epidemiology, provide a powerful tool that can be used to systematically examine an array of dynamic interactions among populations as well as to evaluate altemate disease intervention strategies. The specific objectives in this study were to: a/ examine the interaction of cellular (CD4) and HIV population dynamics and evaluate the impact of the use of combination chemotherapies on viral and CD4 populations (Experiment #1), b/ demonstrate how modelling can be used to evaluate the impact of an intervention (condom use) on reducing the rate of HIV/AIDS (Experiment #2). In this study, we used state transition models and conducted simulation experiments to evaluate various alternatives for the control and/or prevention of HIV/AIDS. The result indicated that combination therapy (double or triple drug therapies) was very effective. The HIV viral population decreased rapidly and remained suppressed for years. On the other hand, the CD4 cell population increased above 400 cells per ml and was maintained above that level for many years. Mono-therapy was not as effective; although the viral load decreased rapidly, it increased to its original levels within a few months. Since condom use is one of the key interventions of HIV/AIDS, we evaluated its use in 25%, 50% and 75% of an adult, sexually active population. Increasing condom use by 50% and 75% above an estimated baseline of 25% reduced the incidence of AIDS by 53% in Blacks, 49% in Hispanics and 43% in Whites. The study shows how a cellular/molecular level model can be incorporated within a macro-epidemiologic systems dynamics model to evaluate a variety of scientific questions such as to see if cellular/molecular level interventions reduce morbidity and mortality rates in HIV.

Anti-HIV Agents↗
PubMed2000

Distinct regions of the chicken p46 polypeptide are required for its in vitro interaction with histones H2B and H4 and histone acetyltransferase-1.

We cloned cDNA encoding the chicken p46 polypeptide, chp46, homologous to the p48 subunit of chicken chromatin assembly factor-1, chCAF-1p48. It comprises 424 amino acids including a putative initiation Met, is a member of the WD protein family, with seven WD repeat motifs, and exhibits 90.3% identity to chCAF-1p48 and 94.3% identity to the human and mouse p46 polypeptides (hup46 and mop46). The in vitro immunoprecipitation experiment established that chp46 interacts with histones H2B and H4 and chicken histone acetyltransferase-1, chHAT-1, whereas hup46 interacts with histones H2A and H4 and chHAT-1 and chCAF-1p48 with histone H4 and chHAT-1. The in vitro immunoprecipitation experiment, involving truncated mutants of chp46, revealed not only that two regions comprising amino acids 33-179 and 375-404 are necessary for its binding to H2B, but also that two regions comprising amino acids 1-32 and 405-424 are necessary for its binding to H4. Furthermore, the GST pulldown affinity assay, involving truncated mutants of chp46, revealed that a region comprising amino acids 359-404 (in fact, 375-404) binds to chHAT-1 in vitro. Taken together, these results indicate not only that chp46 should participate differentially in a number of DNA-utilizing processes through interactions of its distinct regions with chHAT-1 and histones H2B and H4, but also that the proper propeller structure of chp46 is not necessary for its interaction with chHAT-1.

Acetyltransferases↗