Pneumocystis carinii shows DNA homology with the ustomycetous red yeast fungi

Pneumocystis carinii causes life-threatening pneumonia in T-lymphocyte-immunodeficient subjects in transplant and oncology units or with acquired immune deficiency syndrome (AIDS). Recent DNA homology studies show P. carinii to be a fungus. To investigate the biology and epidemiology of this parasite further, we elected to determine for it a more precise taxonomic assignment within the fungal kingdom. We screened a wide range of organisms representing the major orders of fungi using DNA amplification and subsequently sequenced a portion of the mitochondrial gene encoding the large subunit ribosomal RNA. Our data show that the opportunistic pulmonary pathogen P. carinii is closely related to the ustomycetous red yeast fungi, a group which includes organisms that are extensively distributed throughout the environment and which release many widely dispersed airborne spores.     

The human genetic map

The introduction of new technology and increased effort from around the world is driving the completion of the human gene map. In parallel with the creation of the map, we are beginning to see the bio-medical benefits that are a direct consequence of learning more about our own genome.     

Identification and characterization of an {alpha}-mannosidase from Trypanosoma cruzi

In this report we describe the first purification and characterizationof the acid -mannosidase from the human parasite Trypanosomacruzi. The purified enzyme exhibited a native mol. wt of 240000 Da and is apparently composed of four identical subunitsof mol. wt 58 000 Da. Each of the four subunits contains oneN-linked high-mannose-type oligosaccharide. The -mannosidaseexhibited a pH optimum of 3.5 and a pI of 5.9. This low pH optimumand the ability of swainsonine to inhibit its activity suggestthat the -mannosidase is a lysosomal enzyme. Antibodies againstthe T.cruzi enzyme did not react with mammalian lysosomal -mannosidaseand, conversely, antibody against a rat lysosomal -mannosidasedid not react with the T.cruzi enzyme. Thus, the T.cruzi enzymeappears to be distinct from its mammalian counterpart. -mannosidase lysosomal enzyme Trypanosoma cruzi     

The adenine nucleotide translocator of higher plants is synthesized as a large precursor that is processed upon import into mitochondria.

Two maize genes and cDNAs encoding the mitochondrial adenine nucleotide translocator (ANT), a nuclear-encoded inner mitochondrial membrane carrier protein, have previously been isolated in this laboratory. Sequence analysis revealed the existence of much longer open reading frames than the corresponding fungal and mammalian ANT genes. Potato ANT cDNAs have subsequently been isolated and sequenced and alignment of the deduced plant amino acid sequences with the equivalent fungal and mammalian polypeptides indicated that the plant proteins contain N-terminal extensions. When the plant cDNA clones are expressed in vitro they direct the synthesis of precursor proteins that are specifically processed at the N-terminus upon import into isolated mitochondria. N-terminal amino acid sequence data obtained from the native proteins purified from both maize and potato mitochondria has allowed identification of the putative processing sites. Further import analysis has shown that two distinct regions of the maize precursor protein contain targeting information, the 97 amino acids at the N-terminus and the 267 C-terminal amino acids. This is the first report that provides experimental evidence that the adenine nucleotide translocator of higher plants is synthesized as a large precursor protein that is specifically cleaved upon import into mitochondria. Import of ANT into higher plant mitochondria therefore appears to be different to the corresponding process in fungal and mammalian systems where targeting of ANT to mitochondria is mediated by internal signals and there is no N-terminal processing.     

Pastoral dairy marketing and household wealth interactions and their implications for calves and humans in Ethiopia

Surveys of pastoral households in a semi-nomadic Borana community during 1987–1988 were used to test the hypothesis that poorer families living closest to a market town would be most affected by the enhanced opportunity to sell dairy products, which would intensify competition between people and calves for milk and have negative implications for calf management. These poorer families indeed reported the highest rates of milk offtake per cow, and the milk increment was probably sold to purchase more grain for human consumption at the expense of milk intake for the calf. Consequently, this strategy may increase the susceptibility of malnourished calves to disease, especially those from lower-producing dams. Benefits of improved human energy intake from grain and retention of livestock capital must be weighed against risks of calf death and possible malnutrition of people from milk restriction when assessing dairy marketing trade-offs that are most acute for the poor. Opportunity to sell dairy products at favorable terms of trade helps the poorest people survive, and their risks could be mitigated by policies that facilitate grain marketing in the rangelands and interventions that improve calf feeding management, diversify human diets, and create alternative opportunities for women to generate income. The households postulated to be most at risk were identified from a complex, but logical, interaction among factors of distance to market, household wealth, and the quality of milking cows held. This indicates that targeting such needy groups for development assistance may require a more detailed and interdisciplinary analysis of production systems than is commonly practiced.     

Pharmacology of insect GABA receptors

A GABA-operated Cl^– channel that is bicuculline-insensitive is abundant in the nervous tissue of cockroach, in housefly head preparations and thorax/abdomen preparations, and in similar preparations from several insect species. Bicuculline-insensitive GABA-operated Cl^– channels, which are rare in vertebrates, possess sites of action of benzodiazepines, steroids and insecticides that are pharmacologically-distinct from corresponding sites on vertebrate GABA_A receptors. The pharmacological profile of the benzodiazepine-binding site linked to an insect CNS GABA-operated Cl^– channel resembles more closely that of vertebrate peripheral benzodiazepine-binding sites. Six pregnane steroids and certain polychlorocycloalkane insecticides, which are active att-butylbicy-clophosphorothionate (TBPS)-binding sites, also differ in their effectiveness on vertebrate and insect GABA receptors. Radioligand binding and physiological studies indicate that in insects there may be subtypes of the GABA receptor. Molecular biology offers experimental approaches to understanding the basis of this diversity.Special issue dedicated to Dr. Eugene Roberts     

Assessment of spermatozoal function using dual fluorescent staining and flow cytometric analyses

Spermatozoa from bulls, boars, dogs, horses, mice, and men were examined using a fluorogenic stain consisting of the membrane-permeant substrate carboxyfluorescin diacetate (CFDA) and the relatively membrane-impermeant nuclear stain propidium iodide (PI). Three distinct populations of spermatozoa were discernible in samples from each species upon microscopic examination. Individual spermatozoa, presumed to be viable because of their motility, retained products of the fluorescein chromophore throughout the cell. A second population of spermatozoa in which the nuclei stained red with PI retained the green fluorescein fluorophore mainly in the acrosome. A third population, presumed to be degenerate spermatozoa, possessed only red fluorescent nuclei. These populations were quantified using dual parameter flow cytometry in 14 samples of cryopreserved bovine spermatozoa for which fertility and seminal quality data were available. Flow cytometric analyses were highly correlated with other seminal quality measurements. Sequential flow cytometric analyses provided the ability to rapidly quantitate changes in specific fluorescently stained populations. The ability to make rapid quantitative measurements should allow development of new and presumably more reliable information on the functional aspects of spermatozoa.     

The occurrence of cyclic AMP in archaebacteria

Cyclic AMP was found in species representative of the three major groups of the archaebacteria. In Methanobacterium thermoautotrophicum starvation for H2 led to a significant increase in cellular cAMP. The findings suggest that the occurrence of cAMP antedates the divergence of the major kingdoms of biology; the observations also imply that cAMP constitutes a very early regulatory molecule.     

Characterisation of the arrestment responses of Trichogramma evanescens

Summary Contact kairomones and oviposition in a host egg stimulated arrestment behaviour in Trichogramma evanescens, characterised by a reduction in walking speed and increased turning. Previous oviposition experience did not influence a parasitoid's response to contact kairomones, but successive encounters with kairomone patches resulted in parasitoids habituating to the contact chemical. Oviposition on a kairomone patch did not reverse this habituation effect. It was concluded that contact kairomones and host eggs will both contribute independently to the duration of a patch visit. The selection of patches by T. evanescens will depend on its response to kairomones. Results from this study indicate that the application of contact kairomones to field crops will not necessarily increase the probability of parasitoids finding hosts.     

tert–butylhydroperoxide—Induced toxicity in isolated hepatocytes: Contribution of thiol oxidation and lipid peroxidation

Incubation of isolated rat hepatocytes with tert-butylhydroperoxide resulted in marked cytotoxicity preceded by intracellular glutathione depletion and extensive lipid peroxidation. Addition of antioxidants delayed, but did not prevent, this toxicity. A significant decrease in protein-free sulfhydryl groups also, occurred in the presence of tert-butylhydroperoxide; direct oxidation of protein thiols and mixed disulfide formation with glutathione were responsible for this decrease. The involvement of protein thiol depletion in tert-butylhydroperoxide–induced cytotoxicity is suggested by our observation that administration of dithiothreitol, which caused re-reduction of the oxidized sulfhydryl groups and mixed disulfides, efficiently protected the cells from toxicity. Moreover, depletion of intracellular glutathione by pretreatment of the hepatocytes with diethyl maleate accelerated and enhanced the depletion of protein thiols induced by tert-butylhydroperoxide and potentiated cell toxicity even in the absence of lipid peroxidation.