Unusual basement layer in the midgut of gammaridean Niphargus virei Chevreux (Crustacea,Amphipoda)

Summary The basement membrane of the midgut and posterior caeca epithelium in the gammaridean amphipod Niphargus virei Chevreux, 1896 is made of an unusual structure. This basal lamina, properly called basal layer, shows a dense sheet formed by a system of dense hexagonal plates connected by thin filaments. Histochemical studies and enzymatic reactions lead to the conclusion that these structures are proteinaceous, without collagenous protein, and embedded in a neutral polysaccharide matrix. The possible mechanical significance of these mesenteric structures is discussed.     

Light adaptation of bacteriorhodopsin in the presence of valinomycin and potassium. pH-dependence

In the presence of valinomycin and K⁺, bacteriorhodopsin undergoes (i) a decrease of its maximum absorbance, (ii) a blue shift of the maximum wavelength of both the light and the dark adapted forms. However (iii) a normal light adaptation is maintained and (iv) the retinal-retinal interactions are not perturbed. The role of valinomycin as a K⁺-carrier allowing a H⁺-K⁺ competition as well as the stabilization of the deprotonated Schiff-base (linking retinal to the apo-opsin) is shown and discussed.Abbreviations bR bacteriorhodopsin - CD circular dichroism - DA dark-adapted - LA light-adapted - M-412 Meta-intermediate of the bacteriorhodopsin photocycle     

ANTHEPROT: a package for protein sequence analysis using a microcomputer

A simple microcomputer package is described to make the theoreticalanalysis of protein sequences. Several methods designed to comparetwo sequences, to model proteolytic reactions and to predictthe secondary structure, the hydro-phobic/hydrophilic regionsand the potential antigenic sites of proteins have been includedin an Apple II microcomputer software. The package comprises21 programs as well as the secondary structure database of Kabschand Sander (1983). Received on November 24, 1987; accepted on March 8, 1988     

Fertilizer nitrogen budget of Na15NO3 and (15NH4)2SO4 split-applied to winter wheat in microplots on a loam soil

Labelled fertilizer N applied to winter wheat as Na¹⁵NO₃ and (¹⁵NH₄)₂SO₄ at a total N dressing of 100kg ha⁻¹ was used in a microplot balance study to investigate the fate of each split fraction at three growth stages: end of tillering, heading and beginning of flowering. Results indicated that while the percentage utilization of the applied N by the grain and total crop increased considerably from the first to the third split application, these values diminished steadily in the straw. Grain recovery values for the first, second and third split applications were 34.2%, 51.5% and 55.7% for the NO₃ and 32.3%, 48.4% and 52.5% for the NH₄ carrier, respectively. The corresponding recovery values for the whole plant were 54.6%, 67.8% and 69.9% for the NO₃ and 51.7%, 63.5% and 66.1% for the NH₄ carrier. A greater proportion of the fertilizer N applied at the end of tillering stage was found in the vegetative plant components as compared with the grain. The reverse occurred for the N applied at the heading and at the beginning of the flowering stages. The residual fertilizer N found in the soil amounted to 18.0%, 10.4% and 11.6% of the applied NO₃−N and to 22.5%, 12.7% and 15.2% of the applied NH₄−N for the respective split applications. No differences were found for each split application between the two carriers as far as the unaccounted fertilizer N was concerned. The losses were 26.6%, 22.3% and 18.6% of the applied N for the three split applications, respectively. The application of fertilizer N did not lead to any increase in soil N uptake by the crop.     

Purifications of Rat Adrenal Dopamine-β-Hydroxylase: Immunological Analysis of Its Soluble and Membrane-Bound Forms with the Use of an Antibody Raised Against the Soluble Form

Soluble and membrane-bound dopamine-beta-hydroxylases (sDBH and mDBH, respectively) from rat adrenal glands have been purified through concanavalin A-Sepharose chromatography, gel filtration, and ion-exchange high-performance chromatographies. Both sDBH and mDBH were composed by four subunits of apparent molecular weight of 75,000 and showed a native molecular weight of 300,000. This procedure has not allowed us to obtain a sufficient amount of enzyme to immunize a rabbit. A second, more rapid procedure was designed to isolate sDBH, including concanavalin A-Sepharose chromatography and preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A rabbit antiserum was raised against this purified protein. The specificity of the antiserum was demonstrated by neutralization of rat adrenal gland DBH activity, labeling of rat adrenal medulla on histological sections, and, after Western blot, labeling of the 75,000-molecular-weight band in the different fractions associated with DBH activity during purification. The antiserum had a higher affinity for the sDBH denatured by sodium dodecyl sulfate than for the native protein. It had a higher affinity for sDBH than for mDBH. These results strongly suggest the presence of specific hydrophilic epitopes on the sDBH, revealing structural differences between the two hydroxylase forms. Two protein bands were stained on Western blots of crude rat adrenal gland extract. One band had an apparent molecular weight of 75,000, and the other of 82,000. Our results showed that the two proteins contained similar epitopes, an observation suggesting a close structural relationship. The higher-molecular-weight protein could be the 75,000 protein before covalent modifications and cleavage.     

Synergistic and molecular interactions between the formamidine amitraz and copper(II) sulfate,used against the mite Varroa jacobsoni O., a parasite of the honeybee Apis mellifera L.

Toxicological field assays have shown that the shock-treatment efficacy of the formamidine pesticide amitraz, used against the parasitic mite Varroa jacobsoni, is synergistically improved by the administration of copper(II) sulfate through feeding of the honeybees. Amitraz is autoxidized and this process is accompanied by chemiluminescence. The emission is enhanced in the presence of low concentrations of H₂O₂. A dose-related inhibition of the chemiluminescence by CuSO₄ was observed; consistent with the formation of copper-amitraz complexes evidenced in vitro. The results suggest the possibility that a protection of amitraz by cupric ions might be at the origin of the enhancement of its toxicity and thus makes a contribution to the observed synergy.     

Bird and insect pollinators differ in specialization and potential pollination services along disturbance and resource gradients

Combined studies of the communities and interaction networks of bird and insect pollinators are rare, especially along environmental gradients. Here, we determined how disturbance by fire and variation in sugar resources shape pollinator communities and interactions between plants and their pollinating insects and birds. We recorded insect and bird visits to 21 Protea species across 21 study sites and for 2 years in Fynbos ecosystems in the Western Cape, South Africa. We recorded morphological traits of all pollinator species (41 insect and nine bird species). For each site, we obtained estimates of the time since the last fire (range: 2–25 calendar years) and the Protea nectar sugar amount per hectare (range: 74–62 000 g/ha). We tested how post-fire age and sugar amount influence the total interaction frequency, species richness and functional diversity of pollinator communities, as well as pollinator specialization (the effective number of plant partners) and potential pollination services (pollination service index) of insects and birds. We found little variation in the total interaction frequency, species richness and functional diversity of insect and bird pollinator communities, but insect species richness increased with post-fire age. Pollinator specialization and potential pollination services of insects and birds varied differently along the environmental gradients. Bird pollinators visited fewer Protea species at sites with high sugar amount, while there was no such trend for insects. Potential pollination services of insect pollinators to Protea species decreased with increasing post-fire age and resource amounts, whereas potential pollination services of birds remained constant along the environmental gradients. Despite little changes in pollinator communities, our analyses reveal that insect and bird pollinators differ in their specialization on Protea species and show distinct responses to disturbance and resource gradients. Our comparative study of bird and insect pollinators demonstrates that birds may be able to provide more stable pollination services than insects.     

Suppression of allogeneic reactivity in vitm by the syncytiotrophoblast membrane glycocalyx of the human term placenta is carbohydrate dependent

Immunosuppressive factors isolated from trophoblast are knownto block both innate and major histocompatability complex (MHC)-dependentcell-mediated immune responses in vitro and, in some cases,in vivo. We investigated the biochemical nature of these factors,which is presently unknown. Immunosuppressive activity, assessedby inhibition of two-way MLR, was extracted from term syncytiotrophoblastmicrovilli using 3 M KCl. The activity resisted both extensivepronase digestion and heating to 90°C for 1 h, demonstratingthat intact membrane proteins were not required. Although purifiedprotein-linked oligosaccharides released by hydrazinolysis fromthe syncytiotrophoblast membrane were themselves inactive, theyblocked the immunosuppressive activity of the KCl extract. Afterpronase digestion, the activity could be fractionated by TSK55S gel filtration, followed by C18 reverse-phase chromatography.Sequential exoglycosidase digestion of hydrazine-released sugarsof the active fraction demonstrated that it contained neutralN-linked oligomannose and hybrid oligosaccharides, which normallymake up <3% of the total syncytiotrophoblast-derived proteinglycan Library. These glycopeptides of the active fraction wereassociated with membrane phospholipid micelles. The possiblemechanism by which incompletely processed N-linked oligosaccharidesexpressed by a variety of syncytiotrophoblast membrane glycoproteinsmay block allogeneic reactivity when presented as polyvalentsugar groups is discussed. glycoprotein immunosuppression oligosaccharides pregnancy trophoblast