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At least 217 records · Page 12Linked to original sources
PubMed1995

A study of some factors affecting the efficiency of in vitro mussel tissue culture for chromosome preparation.

In the course of a series of cultures of mussel mantle tissue three types of limiting factors to the efficiency of the method were identified. They are concerned with medium composition, and tissue culture and explant harvesting procedures. To reduce their negative effects, three changes with respect to the original technique are proposed: (1) incorporation of chick embryo extract in the place of egg yolk for culture medium enrichment; (2) replacement of 1 mm2 explants by 4 mm2 explants so as to suppress centrifugation, thereby gaining time; and (3) avoiding the use of male mantle tissue when it contains mature spermatozoa since this is cumbersome for slide analysis. Conversely, female mantle tissue can be employed without any disadvantage throughout the year especially as mature oocytes give suitable metaphase plates for meiotic chromosome study.

Animals↗
PubMed1996

Questions and answers to psychological assessment schedules: hidden troubles in 'quality of life' interviews.

Quality of life (QOL) has become a topic of much debate in the learning difficulties literature. Increasing use is made of questionnaire-driven interview schedules in an effort to find out what clients believe in their own words. However, in this paper, the authors argue that the use made of such questionnaires may actually distort interviewees' 'own words' by severely underestimating the degree to which the questions and answers are changed by the subtle dynamics of the interview. In the first ever close examination of what actually happens in a QOL assessment interview, the qualitative insights of conversation analysis are used to show that the typical administration of a well-known instrument will involve: (1) distortions of the questions brought about by the need to paraphrase complex items, and the inevitable use of pre-questions and response listing; and perhaps more disturbingly, (2) distortions of answers brought about by interviewers' pursuit of legitimate answers and non-take-up of interviewees' matters. The authors believe that these difficulties make it hard for researchers to draw conclusions from simple aggregation of recorded responses to this questionnaire, and, perhaps, to any questionnaire using a fixed-response schedule. On the other hand, the kind of close evidence used here may allow inferences to be drawn about clients' feelings of well being, but even so, these will need to be cast in terms which acknowledge the interactive and constructive nature of feeling-avowals.

Humans↗
PubMedDate not supplied

Protection by selenoprotein P in human plasma against peroxynitrite-mediated oxidation and nitration.

In order to study functions of selenoprotein P in human plasma, its level was lowered via two techniques, chromatography on Sepharose-bound heparin, or immunoprecipitation; Western blot analysis showed that both techniques were effective at substantially lowering selenoprotein P levels in plasma. When peroxynitrite was infused to maintain a 0.9 microM steady-state concentration, plasma made deficient in selenoprotein P diminished benzoate hydroxylation significantly less than control plasma. Similar differences were found for protein 3-nitrotyrosine formation, determined by Western blot analysis. Conversely, in a selenoprotein P-enriched plasma preparation obtained via heparin-Sepharose chromatography, protection against benzoate hydroxylation was above controls. Likewise, a supernatant from control plasma that had been exposed to anti-selenoprotein P antibodies was less efficient in preventing oxidation and nitration reactions of peroxynitrite than the supernatant from plasma exposed to a non-specific antibody (rabbit anti-sheep IgG). These data demonstrate a role of selenoprotein P in human plasma in the defense against peroxynitrite.

Blotting, Western↗
PubMed1997

Molecular analysis of gene conversion in spermatids from transgenic mice.

Investigations into the mechanisms and properties of gene conversion in mammals are greatly restricted by the inability to recover all the products of a meiosis. Additionally, the study of this process has been hampered by the lack of visible markers to detect gene conversion, especially when the events are rare. In previous work, we developed a transgenic system for detection and quantitation of gene conversion events in the germline of mice (Murti, J.R., Bumbulis, M., Schimenti, J.C., 1992. High frequency germline gene conversion in transgenic mice. Mol. Cell. Biol. 12, 2545-2552) that could be exploited as an assay for recombinogenic chemicals (Murti, J.R, Schimenti, K.J., Schimenti, J.C., 1994. A recombination-based transgenic mouse system for genotoxicity testing. Mutat. Res. 307, 583-595). A specific intrachromosomal gene conversion event between two complementarily defective lacZ genes resulted in the production of beta-galactosidase in spermatids, enabling a measurement of conversion frequency. Here, we report that the anticancer drug, cisplatin, increased gene conversion in meiotic stage cells in these transgenic mice. Furthermore, a method was developed for direct molecular analysis of transgene conversion events in single or pooled lacZ-positive spermatids. The ability to identify gametes that have undergone a rare gene conversion event, followed by molecular amplification of the recombinant gene, should make it possible to investigate the mechanisms of genetic recombination in mammals in greater detail than previously possible.

Animals↗
PubMed2003

Steady-state and pre-steady-state kinetic analysis of halopropane conversion by a rhodococcus haloalkane dehalogenase.

Haloalkane dehalogenase from Rhodococcus rhodochrous NCIMB 13064 (DhaA) catalyzes the hydrolysis of carbon-halogen bonds in a wide range of haloalkanes. We examined the steady-state and pre-steady-state kinetics of halopropane conversion by DhaA to illuminate mechanistic details of the dehalogenation pathway. Steady-state kinetic analysis of DhaA with a range of halopropanes showed that bromopropanes had higher k(cat) and lower K(M) values than the chlorinated analogues. The kinetic mechanism of dehalogenation was further studied using rapid-quench-flow analysis of 1,3-dibromopropane conversion. This provided a direct measurement of the chemical steps in the reaction mechanism, i.e., cleavage of the carbon-halogen bond and hydrolysis of the covalent alkyl-enzyme intermediate. The results lead to a minimal mechanism consisting of four main steps. The occurrence of a pre-steady-state burst, both for bromide and 3-bromo-1-propanol, suggests that product release is rate-limiting under steady-state conditions. Combining pre-steady-state burst and single-turnover experiments indicated that the rate of carbon-bromine bond cleavage was indeed more than 100-fold higher than the steady-state k(cat). Product release occurred with a rate constant of 3.9 s(-1), a value close to the experimental k(cat) of 2.7 s(-1). Comparing the kinetic mechanism of DhaA with that of the corresponding enzyme from Xanthobacter autotrophicus GJ10 (DhlA) shows that the overall mechanisms are similar. However, whereas in DhlA the rate of halide release represents the slowest step in the catalytic cycle, our results suggest that in DhaA the release of 3-bromo-1-propanol is the slowest step during 1,3-dibromopropane conversion.

Binding Sites↗
PubMed2004

Technical and economical analysis of the conversion of a full-scale scrubber to a biotrickling filter for odor control.

The present paper evaluates the technical and economical feasibility of converting wet chemical scrubbers to biotrickling filters for H2S control at the Orange County Sanitation District (OCSD), California. Results of 8 months of continuous operation of a biotrickling filter treating 16,000 m3 h(-1) of foul air are analyzed. The reactor was operated at a gas contact time of 1.6 to 2.2 seconds reaching H2S elimination capacities up to 105-110 g H2S m3 h(-1), consistently maintaining outlet concentrations well below the regulatory limits (24 h average of 1 ppmv) and demonstrating to be very robust against temporary changes. Also, a cost-benefit analysis of the conversion was performed. Savings from chemicals, energy and water usage compared to a chemical scrubber operated in parallel to the biotrickling filter throughout the project indicated that the payback time of the conversion was about 1.3 years. Cost savings ranged between 40,000 US dollars per year, per scrubber. While the above number may be specific to OCSD conditions, the cost analysis suggests that there is a significant benefit of converting chemical scrubbers to biotrickling filters over a wide range of operating conditions.

Biodegradation, Environmental↗
PubMed2006

Commitment in same-sex relationships: A qualitative analysis of couples' conversations.

Theoretical constructs and meanings of relational commitment for same-sex couples have typically been generalized from heterosexual relationships. Same-sex couples, however, face a unique set of challenges in constructing committed relationships. To expand our knowledge of the meaning of commitment, same-sex couples described their lived experiences in defining and creating a committed relationship. Transcripts of the conversations of 14 same-sex couples (7 male and 7 female couples) were subjected to analysis using the Consensual Qualitative Research (CQR) method (Hill, Thompson, and Williams, 1997). Seven domains emerged, revealing that these same-sex couples constructed the meaning of commitment through comparisons, costs, intra-couple differences, investments, personal and relationship values and ideals, rewards, and sexual boundaries. Unique aspects of commitment are discussed as well as the implications of these findings for future research and service delivery.

Adult↗
PubMed1997

Policy analysis of the conversion of histamine2 antagonists to over-the-counter use.

OBJECTIVES: The authors assess the costs associated with treatment of dyspepsia with histamine2 antagonists versus without availability of over-the-counter (OTC). METHODS: A cost analysis was performed using a decision-analysis model. Patients with an initial episode of dyspepsia were studied. The model includes costs associated with consumption of OTC and prescription (Rx) medications for dyspepsia, physician visits and associated diagnostic testing, time spent for physician visits and diagnostic tests, and hospitalization costs. RESULTS: The model is sensitive to the relative cost of histamine2 antagonists when purchased Rx or OTC, as well as to the efficacy of these drugs in relieving dyspeptic symptoms. For patients with nonulcer dyspepsia (the largest group of likely consumers), the model demonstrates a cost savings if the OTC cost of the medication is slightly less than one third the Rx cost. Costs are similar whether or not histamine2 antagonists are available OTC. If the symptom relief efficacies of histamine2 antagonists are equivalent whether purchased by prescription only or OTC, then the health-care expenditures for a typical patient with dyspepsia are $204 for OTC availability and $203 for Rx-only use. Viewing costs from the perspective of a managed-care organization, expenditures for an episode of dyspepsia are $149 regardless of whether or not histamine2 antagonists are available OTC. Restricting the analysis to patients with underlying nonulcer dyspepsia yields similar results. Variation of numerous assumptions and probabilities other than histamine antagonist cost and efficacy, including costs associated with physician visits and diagnostic tests, and the likelihood of seeking medical care, do not substantially affect the results of the model. CONCLUSIONS: Health-care costs associated with initial treatment of dyspepsia are similar regardless of the availability of histamine2 antagonists OTC. This is due largely to the similar efficacy of these drugs compared with antacids and the predicted increase in diagnostic testing that may result if a patient visits a physician after failure to achieve symptom relief with OTC use of histamine2 antagonists.

Cost Savings↗
PubMed1986

A general method for identifying correct solutions in the quantitative analysis of gene conversion data.

Past attempts to obtain values for meiotic parameters relating to hybrid DNA formation and the correction of mismatched bases in hybrid DNA have not given unique solutions unless various simplifying assumptions were made. A method is given for identifying correct sets of solutions after calculating the frequency of hybrid DNA formation at a heterozygous site and using the fact that closely linked sites within a locus have very similar hybrid DNA formation frequencies. The method is illustrated with simulated data and Sordaria fimicola data; it can also show up incorrect assumptions in analysis. A method is suggested for assessing the importance of double-strand gaps in producing conversions.

Chromatids↗
PubMed1995

New HLA-DPB1 alleles generated by interallelic gene conversion detected by analysis of sperm.

The rate at which allelic diversity at the HLA loci evolves has been the subject of considerable controversy. The patchwork pattern of sequence polymorphism within the second exon of the HLA class II loci, particularly in the DPB1 locus, may have been generated by segmental exchange (gene conversion). We have analysed the frequency of variant DPB1 sequences that have been created by interallelic gene conversion in the germline by screening pools of sperm using PCR amplification and oligonucleotide probe typing. Our results indicate that about 1/10,000 sperm represents a new DPB1 sequence generated by short tracts of segmental exchange (gene conversion) within the second exon, suggesting that interallelic gene conversion may have an important role in generating the extensive allelic diversity at the HLA loci.

Alleles↗
PubMed2006

Force meets chemistry: analysis of mechanochemical conversion in focal adhesions using fluorescence recovery after photobleaching.

Mechanotransduction--the process by which mechanical forces are converted into changes of intracellular biochemistry--is critical for normal cell and tissue function. Integrins facilitate mechanochemical conversion by transferring physical forces from the extracellular matrix, across the cell surface, and to cytoskeletal-associated proteins within focal adhesions. It is likely that force alters biochemistry at these sites by altering molecular binding affinities of a subset of focal adhesion proteins, but this has been difficult to quantify within living cells. Here, we describe how the fluorescence recovery after photobleaching (FRAP) technique can be adapted and used in conjunction with mathematical models to directly measure force-dependent alterations in molecular binding and unbinding rate constants of individual focal adhesion proteins in situ. We review these recent findings, and discuss the strengths and limitations of this approach for analysis of mechanochemical signaling in focal adhesions and other cellular structures. The ability to quantify molecular binding rate constants in the physical context of the living cytoplasm should provide new insight into the molecular basis of cellular mechanotransduction. It also may facilitate future efforts to bridge biological experimentation and mathematical modeling in our quest for a systems biology level description of cell regulation.

Animals↗
PubMed1987

Analysis of proinsulin conversion activated by prior glucose: evidence that glucose stimulates synthesis of the conversion enzyme.

We examined the mechanism by which prior glucose exposure accelerates conversion of proinsulin to insulin in pancreatic islets. Using actinomycin A, introduced at different times after a 3H-leucine pulse to block the intracellular transport of proinsulin, transport was found to be slightly accelerated after prolonged glucose. However, computer simulation of pulse-chase experiments showed that activation of conversion is mostly due to increased converting activity. Measurement of islet procathepsin B by immunoprecipitation indicated synthesis of this enzyme was stimulated about two fold after glucose. Pre-exposure with tunicamycin inhibited the acceleration of conversion, suggesting that the converting system requires glycosylation.

Antimycin A↗
PubMed2000

Analysis of internal conversion coefficients

An extensive database has been assembled that contains the three most widely used sets of calculated internal conversion coefficients (ICC): [Hager R.S., Seltzer E.C., 1968. Internal conversion tables. K-, L-, M-shell Conversion coefficients for Z = 30 to Z = 103, Nucl. Data Tables A4, 1-237; Band I.M., Trzhaskovskaya M.B., 1978. Tables of gamma-ray internal conversion coefficients for the K-, L- and M-shells, 10 < or = Z < or = 104, Special Report of Leningrad Nuclear Physics Institute; Rosel F., Fries H.M., Alder K., Pauli H.C., 1978. Internal conversion coefficients for all atomic shells, At. Data Nucl. Data Tables 21, 91-289] and also includes new Dirac Fock calculations [Band I.M. and Trzhaskovskaya M.B., 1993. Internal conversion coefficients for low-energy nuclear transitions, At. Data Nucl. Data Tables 55, 43-61]. This database is linked to a computer program to plot ICCs and their combinations (sums and ratios) as a function of Z and energy, as well as relative deviations of ICC or their combinations for any pair of tabulated data. Examples of these analyses are presented for the K-shell and total ICCs of the gamma-ray standards [Hansen H.H., 1985. Evaluation of K-shell and total internal conversion coefficients for some selected nuclear transitions, Eur. Appl. Res. Rept. Nucl. Sci. Tech. 11.6 (4) 777-816] and for the K-shell and total ICCs of high multipolarity transitions (total, K-, L-, M-shells of E3 and M3 and K-shell of M4). Experimental data sets are also compared with the theoretical values of these specific calculations.

Journal Article↗
PubMed1998

Analysis of the conversion of delta-(L-alpha-aminoadipoyl)-L-cysteinyl-D-alpha-aminobutyrate by active-site mutants of Aspergillus nidulans isopenicillin N synthase.

BACKGROUND: Penicillins and cephalosporins constitute a major class of clinically useful antibiotics. A key step in their biosynthesis involves the oxidative cyclisation of delta-(Lalpha-aminoadipoyl)-L-cysteinyl-D-valine to isopenicillin N by isopenicillin N synthase (IPNS). This chemically remarkable transformation has been extensively studied using substrate analogues. The conversion of an analogue in which the valine is replaced by alpha-aminobutyrate results in three products, two epimeric penams and a cepham. The ratio of these products in reactions catalysed by four different IPNS isozymes has been used previously to probe the thermicity of the chemical mechanism. But how IPNS restricts the products from the natural substrate to a single penam (isopenicillin N) has remained unknown. RESULTS: A key active-site residue, Leu223, identified according to a model of enzyme-substrate binding, has been altered to sterically less demanding residues. As the steric constraints on the upper part of the active site are reduced, the ratio of the beta-methyl penam to the cepham increases when the alpha-aminobutyrate-containing substrate analogue is used. These results suggest a mechanism for processing of the natural substrate in which IPNS uses steric control to restrict the conformational freedom of an intermediate such that the only product is the penam. CONCLUSIONS: Using steric pressure to control conformation, and hence to disfavour reactions leading to alternate products, is probably the result of evolutionary selection for a biologically active product at the expense of biologically inactive byproducts. It is likely that this sort of enzymatic catalysis is used in situations where substrate conversion is highly exothermic and a variety of products are possible.

Aspergillus nidulans↗