The chromosomes ofAzima tetracantha (Salvadoraceae)

Azima tetracantha has an asymmetrical karyotype with large chromosomes and a large amount of heterochromatin. The haploid number (n = 11) may represent the base number of the family. However, a possible secondary origin of this base number is also considered.     

Band-specific localization of the microsatellite at D13S71 by microdissection and enzymatic amplification.

Microsatellite DNA consists of tandemly repeated simple DNA sequence motifs, the number of these repeats being polymorphic. These recently described polymorphisms are ubiquitously distributed throughout the human genome and are highly informative, making them ideal markers for linkage analysis. Physical localization of these microsatellites is an important prerequisite for aligning physical and genetic maps. We have physically mapped the microsatellite at D13S71, which has previously been assigned to chromosome 13. Band-specific mapping of D13S71 to the distal part of band 13q32, near 13q33, was achieved by microdissection of GTG-banded chromosomes and subsequent enzymatic amplification with a heminested PCR approach. Analysis of a panel of somatic cell hybrids confirmed this localization. The technique presented may also be useful in a variety of complex mapping situations and whenever the precise localization of very small (as small as 70 bp) DNA probes is necessary.     

A region of tissue plasminogen activator that affects plasminogen activation differentially with various fibrin(ogen)-related stimulators.

The dissolution of blood clots by plasmin is normally initiated in vivo by the activation of plasminogen to plasmin through the activity of tissue plasminogen activator (t-PA). The rate of plasminogen activation can be stimulated several orders of magnitude by the presence of fibrin-related proteins. Here we describe the kinetic analysis of both recombinant human t-PA (wild-type) and a t-PA variant produced by site-directed mutagenesis in which the original sequence from amino acids 296 to 299, KHRR, has been altered to AAAA. This tetra-alanine variant form of t-PA, K296A/H297A/R298A/R299A t-PA, we refer to as "KHRR" t-PA here. The plasminogen activating kinetics of wild-type t-PA (Activase alteplase) showed a catalytic efficiency which changed over 100-fold dependent on the stimulator in the assay. The lowest rate was in the absence of a stimulator. The following stimulators showed increasing ability to accelerate the catalytic efficiency of the reaction: fibrinogen, fragments of fibrinogen obtained by digestion with plasmin, fibrin, and slightly degraded fibrin. This increase in efficiency was driven primarily by decreases in the Michaelis constant (KM) of the reaction, whereas the catalytic rate constant (kcat) of the reaction did not change significantly. The "KHRR" variant of t-PA displayed novel kinetics with all stimulators tested. In the absence of a stimulator or with the poorer stimulators (fibrinogen and fibrinogen fragments), the KM values of the reaction with Activase alteplase and "KHRR" t-PA were similar. The kcat however, was lower with "KHRR" t-PA than with wild-type t-PA.(ABSTRACT TRUNCATED AT 250 WORDS)     

The magic-bead concept: an integrated approach to nitrogen removal with co-immobilized micro-organisms

This paper describes both qualitative and quantitative aspects of simultaneous autotrophic nitrification and heterotrophic denitrification by, respectively, the nitrifierNitrisomonas europaea and either of the denitrifiersPseudomonas denitrificans orParacoccus denitrificans co-immobilized in double-layer gel beads. The system is based on the establishment of well-defined oxic and anoxic zones within the cell supports and on physical separation of the nitrifying and denitrifying populations. Nitrification and denitrification rates were obtained from measured bulk concentrations and head-space analysis. The latter analyses showed that ammonia was primarily converted into molecular nitrogen. Nitrous oxide was not detected. High nitrogen removal rates (up to 5.1 mmol N m^–3 gel s^–1) were achieved in continuous reactors under aerobic conditions. The overall rate of nitrogen removal was controlled by the nitrifying step. The approach followed is, in principle, also suitable to the coupling of other oxidative and reductive bioprocesses having complementary metabolic routes. Two-stage bioconversion processes can be thus conducted as if single-staged, which results in more compact reactor systems.     

Sex masks: The double life of female commercial sex workers in Mexico City

The central topic of the article is the divided world of female commercial sex workers (FCSW) in Mexico City. Fourteen focus group sessions were conducted with 133 FCSW from varying socio-economic levels and types of work site, as well as seven individual interviews.FCSW live in a constant double bind, as mother and prostitute, and come into daily contact with society's double standard for women. Reactions include justifying sex work as a better paying employment opportunity for women, as a necessary evil, and as a type of social service, while at the same time hiding their profession from their families. FCSW also live out an archetypal female ambivalence, their selves divided between the mother/saint and the traitor/prostitute.This article defines elements which should be taken into account in culturally appropriate programs for prevention of HIV/AIDS transmission, especially the importance which FCSW give to their role as mothers and promotion of the condom as a physical and symbolic barrier between professional and private life.     

Enrichment of mixed cultures capable of aerobic degradation of 1,2-dibromoethane.

1,2-dibromoethane (DBE) is a common environmental contaminant; it is potentially carcinogenic and has been detected in soil and groundwater supplies. Most of the biodegradation studies to date have been performed under anaerobic conditions or in the context of soil remediation, where the pollutant concentration was in the parts per billion range. In this work a mixed bacterial culture capable of complete aerobic mineralization of concentrations of DBE up to 1 g liter(-1) under well-controlled laboratory conditions was enriched. In order to verify biodegradation, formation of biodegradation products as well as the disappearance of DBE from the biological medium were measured. Complete mineralization was verified by measuring stoichiometric release of the biodegradation products. This mixed culture was found to be capable of degrading other halogenated compounds, including bromoethanol, the degradation of which has not been reported previously.     

Extraction and biodegradation of a toxic volatile organic compound (1,2-dichloroethane) from waste-water in a membrane bioreactor

An extractive membrane bioreactor has been used to treat a synthetic waste-water containing a toxic volatile organic compound, 1,2-dichloroethane (DCE). Biofilms growing on the surface of the membrane tubes biodegrade DCE while avoiding direct contact between the DCE and the aerating gas. This reduces air stripping by more than an order of magnitude (from 30–35% of the DCE entering the system to less than 1%) relative to conventional aerated bioreactors. Over 99% removal of DCE from a waste-water containing 1600 mg l^–1 of DCE was achieved at waste-water residence times of 0.75 h. Biodegradation was verified as the removal mechanism through measurements of CO₂ and chloride ion evolution in the bioreactor. No DCE was detected in the biomedium over the operating period. The diffusion-reaction phenomena occurring in the biofilm have been described by a mathematical model, which provides calculated solutions that support the experimental results by predicting that all DCE is biodegraded within the biofilm. Experimentally, however, the rate of DCE degradation in the biofilm was found to be independent of O₂ concentration, while the model predictions point to O₂ being limiting.