Ribosomal DNA variation in the grasshopper, Dichroplus elongatus.

We report an RFLP analysis of ribosomal DNA variation in natural populations of the grasshopper, Dichroplus elongatus, previously analyzed for mitochondrial DNA variation. DNA samples were digested with five restriction enzymes, BamHI, EcoRI, HindIII, PstI, and XbaI. BamHI was the only enzyme that showed no variation. The remaining enzymes showed fragment size variation at both intra- and interpopulation levels. Stepwise regression analysis revealed that the average number of length variants per individual is significantly associated with altitude. Moreover, the same analysis indicated that the frequency of some restriction variants exhibits a significant regression on both geographic and climatic variables. The intra- and interpopulation variability of rDNA was analysed by Lynch's and Hedrick's similarity indices using presence or absence of a fragment and band intensities, respectively. The corresponding neighbour-joining (N-J) trees based on Lynch's and Hedrick's genetic distances resulted in similar topologies. However, these trees were not in agreement with the N-J dendrogram obtained from mtDNA data previously reported by Clemente et al. (2000). The disagreement between mtDNA and rDNA phenograms along with the observed correlation between rDNA variability and geographical and climatic variables suggest some form of selection, besides genetic drift and migration, is involved in the pattern of rDNA variation.     

Activation of serine protease subtilisin Carlsberg in organic solvents: combined effect of methyl-β-cyclodextrin and water

Methyl -cyclodextrin (MCD) increased the activity and enantioselectivity of lyophilized subtilisin suspended in dry THF and acetonitrile in two transesterification model reactions. These beneficial improvements were diminished by the addition of water, in contrast to the observation that water activates subtilisin lyophilized from buffer alone. For example, the initial rate for the S enantiomer in the transesterification of vinylbutyrate with (±)-1-phenylethanol (sec-phenethylalcohol) decreased ca. 4-fold and the enantioselectivity from 59 to 40 when 0.1% (v/v) of water was added to THF.     

Site-directed mutagenesis of Glu-297 from the α-polypeptide of Phaseolus vulgaris glutamine synthetase alters kinetic and structural properties and confers resistance to L-methionine sulfoximine

In this paper we examine the functionality of Glu-297 from the -polypeptide of Phaseolus vulgaris glutamine synthetase (EC 6.3.1.2). For this purpose, the gln cDNA was recombinantly expressed in Escherichia coli, and site-directed mutants constructed, in which this residue was replaced by alanine. The level of glutamine synthetase transferase catalytic activity in the mutant strain was 70-fold lower while biosynthetic activity remained practically unaffected. Kinetic parameters for both enzyme activities were not greatly altered except for the K_m for ammonium in biosynthetic activity, which increased 100-fold. A similar result was reported when mutagenizing Glu-327 from E. coli glutamine synthetase, a residue shown to be present at the active site. This suggests that the Glu residue mutated in the higher-plant enzyme could develop a similar catalytic role to that of bacteria. Another characteristic feature of the mutant protein was its higher resistance to inhibition of the biosynthetic activity by L-methionine sulfoximine, a typical inhibitor of glutamine synthetase. In addition, we show that immunoreactivity of the glutamine synthetase mutant protein, both under native and denaturing conditions, is similar to the wild type, indicating that no deep conformational changes were produced as a consequence of the introduced mutation. However, structural changes in the active site can be predicted from alterations detected in the behaviour of the mutant protein towards affinity chromatography on 2,5-ADP-Sepharose, as compared to the wild type. Nevertheless, complementation of an E. coli glnA mutation indicated that the E297A mutant enzyme was physiologically functional.     

Above-ground biomass and species richness in a Mediterranean salt marsh

Abstract. Species composition, above-ground biomass and diversity of herbaceous communities were recorded in 50 sites on the upper salt marsh of the Guadalquivir delta (SW Spain). Through Canonical Correspondence Analysis relationships were shown between plant-species characteristics abundance and environmental variables. Seven community types were distinguished and related to hydro logical regime and physical and chemical soil parameters. The higher species richness was associated with moderate values of above-ground biomass (Biomass at maximum diversity, BMD = 302 g/m²). Salinity was negatively correlated with species richness. There was no significant correlation with total above-ground biomass. Water regime and soil nutrient (Ca, Mg) content were significant predictors of the community above-ground biomass.     

Siderophore synthesis in Klebsiella pneumoniae and Shigella sonnei during iron deficiency.

Klebsiella pneumoniae 298/53 and Shigella sonnei 43-GG9 exhibited restricted growth and enterochelin synthesis only under iron-deficient conditions. S. sonnei also produced an unidentified secondary hydroxamate siderophore.     

SILVER DEPOSITION IN THE CENTRAL NERVOUS SYSTEM AND THE HEMATOENCEPHALIC BARRIER STUDIED WITH THE ELECTRON MICROSCOPE

For the purpose of studying the hematoencephalic barrier as it is concerned with silver circulating in the blood stream, silver nitrate was vitally administered to rats in their drinking water over periods of 6 to 8 months. The cerebrum, cerebellum, medulla, area postrema, and choroid plexus were prepared for light and electron microscopy. Silver deposition was found in the perivascular spaces in the choroid plexus, area postrema, in the medulla surrounding the area postrema, and in minute quantities in the cerebrum, cerebellum, and most of the medulla. Two levels of the hematoencephalic barrier were apparently demonstrated in our investigations. The endothelial linings of the vessels in the cerebrum, cerebellum, and medulla constitute the first threshold of the hematoencephalic barrier (specifically here, blood-brain barrier). The cell membranes adjacent to the perivascular spaces form the second threshold, as follows:—the neuroglial cell membranes in the cerebrum, cerebellum, and medulla (blood-brain barrier); the membranes of the neuroglial cells in the area postrema (blood-brain barrier); and the membranes of the epithelial cells of the choroid plexus (blood-cerebrospinal fluid barrier). This study deals with silver deposition and does not infer that the penetration of ionic silver, if present in the blood stream, would necessarily be limited to the regions described. Bleb-like structures were observed to cover the epithelial cell surfaces in the choroid plexus. They may be cellular projections increasing the cell surface area or they may be secretory droplets.     

Growth, water relations and photosynthesis of seedlings and resprouts after fire

Seasonal patterns of growth, water relations, photosynthesis and leaf characteristics were compared between obligate seeders (Cistus monspeliensis and Cistus ladanifer) and resprouters (Arbutus unedo and Pistacia lentiscus) from the first to the second year after fire. We hypothesized that seedlings would be more water-limited than resprouts due to their shallower root systems. Regarding water use strategies, Cistus species are drought semi-deciduous and A. unedo and P. lentiscus are evergreen sclerophylls, therefore, comparisons were based on the relative deviation from mature conspecific plants. Seedlings and resprouts had higher shoot elongation and leaf production than mature plants, and over an extended period. Differences from mature plants were larger in resprouts, with two-fold transpiration, leaf conductance and photosynthesis in late spring/early summer. Seedlings of C. monspeliensis exhibited higher transpiration and leaf conductance than mature plants, while those of C. ladanifer only exhibited higher water potential. Growth increments and ameliorated water relations and photosynthesis after fire were attributed to an increase in water and nutrient availability. The small differences in water relations and photosynthesis between seedlings and mature conspecifics are in accordance with the prediction of seedlings experiencing higher water limitation than resprouts. We attribute these results to differences in root systems: resprouters benefited from an increase in root/shoot ratios and the presence of deep roots whereas Cistus seedlings relied on very shallow roots, which cannot provide assess to deep water during summer. Nevertheless, seedlings did not show evidence of experiencing a more severe water limitation than mature conspecifics, which we attributed to the presence of efficient mechanisms of avoiding and tolerating water stress. The results are discussed in relation to post-fire demography of seeders and resprouters in Mediterranean communities.     

Macrocyclic inhibitors of the malarial aspartic proteases plasmepsin I, II, and IV

The first macrocyclic inhibitor of the Plasmodium falciparum aspartic proteases plasmepsin I, II, and IV with considerable selectivity over the human aspartic protease cathepsin D has been identified. A series of macrocyclic compounds were designed and synthesized. Cyclizations were accomplished using ring-closing metathesis with the second generation Grubbs catalyst. These compounds contain either a 13-membered or a 16-membered macrocycle and incorporate a 1,2-dihydroxyethylene as transition state mimicking unit. The binding mode of this new class of compounds was predicted with automated docking and molecular dynamics simulations, with an estimation of the binding affinities through the linear interaction energy (LIE) method.     

Taxonomic reports of Homeacanthoidea (Eucestoda: Trypanorhyncha) in Lamnid and Sphyrnid elasmobranchs collected off the coast of Santa Catarina, Brazil

Elasmobranch specimens of lamnid and sphyrnid captured in 1999 in the State of Santa Catarina, Brazil, were parasitized with homeacanthoid trypanorhynch cestodes: Isurus oxyrinchus Rafinesque, 1810 with Nybelinia lingualis (Cuvier, 1817) Dollfus, 1929; Sphyrna zygaena (Linnaeus, 1758) with Heteronybelinia rougetcampanae (Dollfus, 1960) Palm, 1999. New details of internal morphology and/or scolex and/or proglottid surface ultrastructure are given. Adults of N. lingualis are reported for the first time in the Brazilian coast.