Molybdopterin guanine dinucleotide cofactor in Synechococcus sp. nitrate reductase: identification of mobA and isolation of a putative moeB gene

Cathepsin B and other lysosomal cysteine proteinases are synthesized as inactive zymogens, which are converted to their mature forms by other proteases or by autocatalytic processing. Procathepsin B autoactivation was shown in vitro at pH 4.5 to be a bimolecular process with K(s) and k(cat) values of 2.1+/-0.9 microM and 0.12+/-0.02 s(-1)6.0. However, in the presence of 0.5 microg/ml of dextran sulfate, relatively rapid processing is observed even at pH 6.5 (t(1/2) approximately 90 min), suggesting that glycosaminoglycans are involved in in vivo processing of lysosomal cysteine proteases.     

Site-directed mutagenesis of cytochrome c6 from Synechocystis sp. PCC 6803. The heme protein possesses a negatively charged area that may be isofunctional with the acidic patch of plastocyanin

This paper reports the first site-directed mutagenesis analysis of any cytochrome c6, a heme protein that performs the same function as the copper-protein plastocyanin in the electron transport chain of photosynthetic organisms. Photosystem I reduction by the mutants of cytochrome c6 from the cyanobacterium Synechocystis sp. PCC 6803 has been studied by laser flash absorption spectroscopy. Their kinetic efficiency and thermodynamic properties have been compared with those of plastocyanin mutants from the same organism. Such a comparative study reveals that aspartates at positions 70 and 72 in cytochrome c6 are located in an acidic patch that may be isofunctional with the well known "south-east" patch of plastocyanin. Calculations of surface electrostatic potential distribution in the mutants of cytochrome c6 and plastocyanin indicate that the changes in protein reactivity depend on the surface electrostatic potential pattern rather than on the net charge modification induced by mutagenesis. Phe-64, which is close to the heme group and may be the counterpart of Tyr-83 in plastocyanin, does not appear to be involved in the electron transfer to photosystem I. In contrast, Arg-67, which is at the edge of the cytochrome c6 acidic area, seems to be crucial for the interaction with the reaction center.     

Genomic compatibility between two phyllotine rodent species evaluated through their hybrids

In order to investigate the genomic compatibility between allopatric rodent species, Phyllotis darwini and Phyllotis magister, we have studied several cytogenetic and reproductive features of their laboratory hybrids. Of thirty-one pairings between species, only five were successful, producing eleven newborns. Like parents, hybrids had 38 metacentric chromosomes, except for the subtelocentric Y chromosome inherited from P. magister. There was almost total C and G band correspondence between homeologous autosomes. However, parental sex chromosomes had different morphology, C and G bands. Ag-NOR bands appeared as small telomeric Ag+ regions, distributed in four chromosomal pairs of darwini, three of magister and four homeologous chromosomes of the hybrids. The three forms had similar indexes of NOR activity per cell, in spite of the variability in NOR expression which was always detected. Usually, only one member of parental homologous chromosomes showed AgNOR+; nevertheless, both homeologous chromosomes were active in many hybrid cells. The frequencies of cells that expressed their ribosomal genes in the two homologous or homeologous NOR chromosomes were similar in parental and hybrid cells. These results strongly suggest that ribosomal genes of both parental genomes would function codominantly in the hybrids. The gonad histological and morphometric analyses showed that hybrids conformed to Haldane's rule, since females were fertile and males were infertile. Our results indicate that P. darwini and P. magister genomes can function in relative harmony and compatibility when they are placed together in their laboratory generated hybrids, suggesting that these species have few genetic differences, probably because they have recently diverged.     

Covariance and decoupling of floral and vegetative traits in nine Neotropical plants: a re-evaluation of Berg's correlation-pleiades concept

Nearly forty years ago R. L. Berg proposed that plants with specialized pollination ecology evolve genetic and developmental systems that decouple floral morphology from phenotypic variation in vegetative traits. These species evolve separate floral and vegetative trait clusters, or as she termed them, "correlation pleiades." The predictions of this hypothesis have been generally supported, but only a small sample of temperate-zone herb and grass species has been tested. To further evaluate this hypothesis, especially its applicability to plants of other growth forms, we examined the patterns of phenotypic variation and covariation of floral and vegetative traits in nine species of Neotropical plants. We recognized seven specific predictions of Berg's hypothesis. Our results supported some predictions but not others. Species with specialized pollination systems usually had floral traits decoupled (weak correlation; Canna and Eichornia) or buffered (relationship with shallow proportional slope; Calathea and Canna) from variation in vegetative traits. However, the same trend was also observed in three species with unspecialized pollination systems (Echinodorus, Muntingia, and Wedelia). One species with unspecialized pollination (Croton) and one wind-pollinated species (Cyperus) showed no decoupling or buffering, as predicted. While species with specialized pollination usually showed lower coefficients of variation for floral traits than vegetative traits (as predicted), the same was also true of species with unspecialized or wind pollination (unlike our prediction). Species with specialized pollination showed less variation in floral traits than did species with unspecialized or wind pollination, as predicted. However, the same was true of the corresponding vegetative traits, which was unexpected. Also in contrast to our prediction, plants with specialized pollination systems did not exhibit tighter phenotypic integration of floral characters than did species with generalized pollination systems. We conclude that the patterns of morphological integration among floral traits and between floral and vegetative traits tend to be species specific, not easily predicted from pollination ecology, and generally more complicated than R. L. Berg envisaged.     

Spectroscopic characterization of the heme-binding sites in Plasmodium falciparum histidine-rich protein 2

Proteolysis of hemoglobin provides an essential nutrient source for the malaria parasite Plasmodium falciparum during the intraerythrocytic stage of the parasite's lifecycle. Detoxification of the liberated heme occurs through a unique heme polymerization pathway, leading to the formation of hemozoin. Heme polymerization has been demonstrated in the presence of P. falciparum histidine-rich protein 2 (PfHRP2) [Sullivan, D. J., Gluzman, I. Y., and Goldberg, D. E. (1996) Science 271, 219-221]; however, the molecular role that PfHRP2 plays in this polymerization is currently unknown. PfHRP2 is a 30 kDa protein composed of several His-His-Ala-His-His-Ala-Ala-Asp repeats and is present in the parasite food vacuole, the site of hemoglobin degradation and heme polymerization. We found that, at pH 7.0, PfHRP2 forms a saturable complex with heme, with a PfHRP2 to heme stoichiometry of 1:50. Spectroscopic characterization of heme binding by electronic absorption, resonance Raman, and EPR has shown that bound hemes share remarkably similar heme environments as >95% of all bound hemes are six-coordinate, low-spin, and bis-histidyl ligated. The PfHRP2-ferric heme complex at pH 5.5 (pH of the food vacuole) has the same heme spin state and coordination as observed at pH 7.0; however, polymerization occurs as heme saturation is approached. Therefore, formation of a PfHRP2-heme complex appears to be a requisite step in the formation of hemozoin.     

Hypoosmotic test in equine spermatozoa

The aim of the study was to evaluate equine sperm membrane integrity using the hypoosmotic swelling (HOS) test and to correlate this test with different sperm parameters in raw and frozen thawed semen. The HOS solutions were made with fructose, sucrose, lactose and sodium citrate each at 300, 150, 100, 50 and 25 mosm. Maximum numbers of swollen spermatozoa were observed in solutions of fructose, sucrose and lactose each at 100, 50 and 25 mosm. Correlations between progressive motility, morphologically normal spermatozoa and the HOS test were r = 0.75 and r = 0.51 in raw semen and r = 0.26 and r = -0.22 in frozen-thawed semen. The correlation between HOS and percentage of intact membranes with the fluorescent stain was r = 0.32 in frozen-thawed semen. The HOS test is a simple and accessible method which could be used as a complement to routine equine semen analysis. It has the added advantages of being less susceptible to the immediate effects of cold shock and of evaluating individual spermatozoa rather than the population as a whole, as does progressive motility.     

Pulmonary aspergillosis outbreak in Rhea americana in Southern Brazil

Commercial raising of rheas is currently in expansion in the south of Brazil, and many diseases previously restricted to other avian species are currently emerging on rhea farms, especially as a result of careless management of these animals. The objective of the present article is to report a pulmonary aspergillosis outbreak that occurred in great rhea (Rhea americana) in the south of Brazil. About 50 birds aged 30 to 60 days died suddenly and one of them was submitted to autopsy which revealed the presence of white caseous nodules 0.5 mm in diameter occupying 95% of the lung area. One lung was sent to the Federal University of Santa Maria for histopathological and mycological analyses. Histopathological analysis revealed multifocal areas with necrosis and inflammatory infiltrates and the presence of fungal hyphae, giant cells and fibrous tissue proliferation at the periphery. Aspergillus fumigatus was recovered as pure culture from all culture media. This appears to be the first report of aspergillosis among great rhea in Brazil and the second in the world.     

Model for Transition from Waves to Synchrony in the Olfactory Lobe of Limax

A biophysical model for the interactions between bursting (B) cells and nonbursting (NB) cells in the procerebral lobe of Limax is developed and tested. Phase-sensitivity of the NB cells is exhibited due to the strong inhibition from the rhythmically bursting B cells. Electrical and chemical junctions coupled with a parameter gradient lead to sustained periodic waves in the lobe. Excitatory interactions between the NB cells, which rarely fire, lead to stimulus evoked synchrony in the lobe oscillations. A novel calcium current is suggested to explain the effects of nitric oxide (NO) on the lobe. Gap junctions are shown both experimentally and through simulations to be required for the oscillating field potentials.     

Characterization of the First VanB Vancomycin-Resistant <Emphasis Type="Italic">Enterococcus faecium</Emphasis> Isolated in a Spanish Hospital

We report the detection and characterization of the first vancomycin-resistant VanB-type Enterococcus faecium to be isolated in a Spanish hospital. Sequence analysis of the vanB gene showed that this isolate belonged to subtype vanB2. Moreover, PCR amplification analysis indicated that the vanB gene cluster was linked to a Tn5382-like transposon.     

Prey stage preference and functional response of Euseius hibisci to Tetranychus urticae (Acari: Phytoseiidae, Tetranychidae)

The aims of this study were: (a) determine the prey stage preference of female Euseius hibisci (Chant) (Phytoseiidae) at constant densities of different stages of Tetranychus urticae Koch (Tetranychidae), (b) assess the functional response of the predator females to the varying densities of eggs, larvae, or protonymphs of T. urticae, and (c) estimate the functional response of E. hibisci when pollen of Ligustrum ovalifolium was present as well. We conducted experiments on excised pieces of strawberry leaf arenas (Fragaria ananassa) under laboratory conditions of 25 ± 2 °C, 60 ± 5% RH and 12 h photophase. Our results indicated that the predator consumed significantly more prey eggs than other prey stages. Consumption of prey deutonymphs and adults was so low that they were excluded from the non-choice functional response experiments. The functional response on all food items was of type II. The two parameters of the functional response were estimated for each prey type by means of the adjusted non-linear regression model. The highest estimated value a (instantaneous rate of discovery) and the lowest value of T_h (handling time, including digestion) were found for the predator feeding on prey eggs, and a was lowest and T_h highest when fed protonymphs. Using the jack-knife method, the values for the functional response parameters were estimated. The values of a and T_h produced by the model were similar among all prey types except for the eggs, which were different. Using pollen simultaneously with prey larvae decreased the consumption of the latter over the full range of prey densities The suitability of this predator for biological control of T. urticae on strawberry is discussed.