Heat-induced redistribution of disulfide bonds in milk proteins. 1. Bovine beta-lactoglobulin

Changes in the structure and chemistry of beta-lactoglobulin (beta-LG) play an important role in the processing and functionality of milk products. In model beta-LG systems, there is evidence that the aggregates of heated beta-LG are held together by a mixture of intermolecular non-covalent association and heat-induced non-native disulfide bonds. Although a number of non-native disulfide bonds have been identified, little is known about the initial inter- and intramolecular disulfide bond rearrangements that occur as a result of heating. These interchange reactions were explored by examining the products of heat treatment to determine the novel disulfide bonds that form in the heated beta-LG aggregates. The native protein and heat-induced aggregates were hydrolyzed by trypsin, and the resulting peptides, before and after reduction with dithiothreitol, were separated by high-performance liquid chromatography and their identities confirmed by electrospray ionization mass spectrometry. Comparisons of these peptide patterns showed that some of the Cys160 was in the reduced form in heated beta-LG aggregates, indicating that the Cys160-Cys66 disulfide bond had been broken during heating. This finding suggests that disulfide bond interchange reactions between beta-LG non-native monomers, or polymers, and other proteins could occur largely via Cys160.     

Determination of albendazole and its major metabolites in the muscle tissues of Atlantic salmon,tilapia, and rainbow trout by high performance liquid chromatography with fluorometric detection

A liquid chromatographic procedure for the determination of albendazole ([5-(propylthio)-1H-benzimidazol-2yl]carbamic acid methyl ester) and its major metabolites, albendazole sulfoxide, albendazole sulfone, and albendazole-2- aminosulfone in rainbow trout, tilapia, and salmon muscle with adhering skin tissue is described. The muscle tissue samples are made alkaline with potassium carbonate and extracted with ethyl acetate. The extracts are further subjected to cleanup by utilizing a number of liquid-liquid extraction steps. After solvent evaporation, the residue is reconstituted in mobile phase and chromatographed. The chromatography is carried out on a reversed phase Luna C(18) column, using acetonitrile/methanol/buffer as a mobile phase and a fluorescence detector. The average recoveries from the fortified muscle tissue of the three fish species for albendazole (25-100 ppb), albendazole sulfoxide (15.5-62 ppb), albendazole sulfone (1-10 ppb), and albendazole-2- aminosulfone (10-100 ppb) were 94, 77, 82, and 67%, respectively. The average CV for each compound was < or =10%. The procedure was validated and then applied to the determination of albendazole and its three major metabolites in the muscle tissue of the three fish species obtained after orally dosing with albendazole.     

Are cadmium, lead and mercury concentrations in mosses across Europe primarily determined by atmospheric deposition of these metals?

Purpose

This study aimed at investigating correlations between heavy metal concentrations in mosses and modelled deposition values as well as other site-specific and regional characteristics to determine which factors primarily affect cadmium, lead and mercury concentrations in mosses. The resulting relationships could potentially be used to enhance the spatial resolution of heavy metal deposition maps across Europe.

Materials and methods

Modelled heavy metal deposition data and data on the concentration of heavy metals in naturally growing mosses were integrated into a geographic information system and analysed by means of bivariate rank correlation analysis and multivariate decision trees. Modelled deposition data were validated annually with deposition measurements at up to 63 EMEP measurement stations within the European Monitoring and Evaluation Programme (EMEP), and mosses were collected at up to 7,000 sites at 5-year intervals between 1990 and 2005.

Results and discussion

Moderate to high correlations were found between cadmium and lead concentrations in mosses and modelled atmospheric deposition of these metals: Spearman rank correlation coefficients were between 0.62 and 0.67, and 0.67 and 0.73 for cadmium and lead, respectively (p?<?0.001). Multivariate decision tree analyses showed that cadmium and lead concentrations in mosses were primarily determined by the atmospheric deposition of these metals, followed by emissions of the metals. Low to very low correlations were observed between mercury concentrations in mosses and modelled atmospheric deposition of mercury. According to the multivariate analyses, spatial variations of the mercury concentration in mosses was primarily associated with the sampled moss species and not with the modelled deposition, but regional differences in the atmospheric chemistry of mercury and corresponding interactions with the moss may also be involved.

Conclusions

At least for cadmium and lead, concentrations in mosses are a valuable tool in determining and mapping the spatial variation in atmospheric deposition across Europe at a high spatial resolution. For mercury, more studies are needed to elucidate interactions of different chemical species with the moss.     

Quantifying functional connectivity: Experimental evidence for patch-specific resistance in the Natterjack toad (Bufo calamita)

Despite the importance assigned to inter-patch movements in fragmented systems, the structure of landscape between suitable habitat patches, the matrix, is often considered as to be of minor interest, or totally ignored. Consequently, models predicting metapopulation dynamics typically assume that dispersal and movement abilities are independent of the composition of the matrix. The predictions of such models should be invalided if that crucial assumption is unverified. In order to test the hypothesis of a patch-specific resistance, we led an experimental study to assess the matrix effects on the movement ability of juvenile Natterjack toads (Bufo calamita). The movement behaviour of first year toadlets, the dispersal stage in this species, was investigated in an arena experiment. Toadlet mobility was assessed in five landscape components that were mimicked in the lab: sandy soil, road, forest, agricultural field, and pasture. We analysed several movement components including move length, speed, efficiency and turning angle distribution. Our results showed that movement ability was strongly affected by the land cover, even if body size modulated the behavioural responses of toadlets. Performances were the best in the arenas mimicking sand and roads, and the worst in the forest arena, toadlet moves being three to five times less effective in the latter. The mobility was intermediate in the two other arenas. We propose here a new method to quantify functional connectivity, based on quantitative estimates of relative values for resistance of landscape components. This method offers a reliable alternative for resistance value estimates to subjective expert advice or inference from genetic population structure.     

Use of mid‐infrared spectroscopy in the diffuse‐reflectance mode for the prediction of the composition of organic matter in soil and litter

Mid‐infrared spectroscopy (MIRS) is assumed to be superior to near‐infrared spectroscopy (NIRS) for the prediction of soil constituents, but its usefulness is still not sufficiently explored. The objective of this study was to evaluate the ability of MIRS to predict the chemical and biological properties of organic matter in soils and litter. Reflectance spectra of the mid‐infrared region including part of the near‐infrared region (7000–400 cm^–1) were recorded for 56 soil and litter samples from agricultural and forest sites. Spectra were used to predict general and biological characteristics of the samples as well as the C composition which was measured by ¹³C CPMAS‐NMR spectroscopy. A partial least‐square method and cross‐validation were used to develop equations for the different constituents over selected spectra ranges after several mathematical treatments of the spectra. Mid‐infrared spectroscopy predicted well the C : N ratio: the modeling efficiency EF was 0.95, the regression coefficient (a) of a linear regression (measured against predicted values) was 1.0, and the correlation coefficient (r) was 0.98. Satisfactorily (EF ≥ 0.70, 0.8 ≤ a ≤ 1.2, r ≥ 0.80) assessed were the contents of C, N, and lignin, the production of dissolved organic carbon, and the contents of carbonyl C, aromatic C, O‐alkyl C, and alkyl C. However, the N mineralization rate, the microbial biomass and the alkyl–to–aromatic C ratio were predicted less satisfactorily (EF < 0.70). Limiting the sample set to mineral soils did generally not result in improved predictions. The good and satisfactory predictions reported above indicate a marked usefulness of MIRS in the assessment of chemical characteristics of soils and litter, but the accuracies of the MIRS predictions in the diffuse‐reflectance mode were generally not superior to those of NIRS.     

Antibody domain exchange is an immunological solution to carbohydrate cluster recognition

Human antibody 2G12 neutralizes a broad range of human immunodeficiency virus type 1 (HIV-1) isolates by binding an unusually dense cluster of carbohydrate moieties on the "silent" face of the gp120 envelope glycoprotein. Crystal structures of Fab 2G12 and its complexes with the disaccharide Manalpha1-2Man and with the oligosaccharide Man9GlcNAc2 revealed that two Fabs assemble into an interlocked VH domain-swapped dimer. Further biochemical, biophysical, and mutagenesis data strongly support a Fab-dimerized antibody as the prevalent form that recognizes gp120. The extraordinary configuration of this antibody provides an extended surface, with newly described binding sites, for multivalent interaction with a conserved cluster of oligomannose type sugars on the surface of gp120. The unique interdigitation of Fab domains within an antibody uncovers a previously unappreciated mechanism for high-affinity recognition of carbohydrate or other repeating epitopes on cell or microbial surfaces.