Use of response surface methodology for the optimization of the lipase-catalyzed synthesis of mannosyl myristate in pure ionic liquid

The purpose of the present study is to find the conditions allowing to reach the highest 24 h-yield (24 h-η) for the synthesis of mannosyl myristate catalyzed by the immobilized lipase B from Candida antarctica (Novozym^® 435) in the ionic liquid (IL) [Bmpyrr][TFO] (1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate). A full factorial design (FFD) was used in order to study the influence of three variables (temperature, mannose/vinyl myristate ratio and total substrate quantity) on the 24 h-η. This design led to a model based on a second order polynomial response function. The resulting predicted contour plots have shown that the highest 24 h-η should be obtained with high temperatures, low sugar/vinyl ester molar ratio and intermediate total substrate quantities (mmol). The model has been successfully verified and experimentally confirmed at the optimal conditions of 80 °C, substrate molar ratio of 1/10 and total substrate quantity of 0.26 mmol leading to the highest predicted 24 h-η of 72.2%.     

A novel non line-of-sight method for coating hydroxyapatite onto the surfaces of support materials by biomineralization

A novel method is described for the non line-of-sight coating of hydroxyapatite onto polyurethane reticulated foam and titanium discs. This utilises a biofilm of Serratia sp. NCIMB 40259 which, when challenged with a solution containing calcium chloride and phosphatase substrate, manufactures biofilm-bound material identified as hydroxyapatite by X-ray powder diffraction analysis. Non-invasive magnetic resonance imaging was used to visualize the biofilm coating throughout the foam labyrinth and to measure the thickness of the film within reticulated foam cubes in situ. The film developed within the cube matrices was similar to that measured on the surface of a glass slide. Using LaPO(4) deposition as a model system the metallised biofilm was visualised in two-dimensional slices throughout three-dimensional images acquired by magnetic resonance imaging. A similar encrustation of hydroxyapatite on the surface of biofilm grown on titanium discs was confirmed by scanning electron microscopy. Potential applications for bio-hydroxyapatite as possible bone implant precursors are discussed.     

The role of site-specific N-glycosylation in secretion of soluble forms of rabies virus glycoprotein

Rabies virus glycoprotein is important in the biology and pathogenesis of neurotropic rabies virus infection. This transmembrane glycoprotein is the only viral protein on the surface of virus particles, is the viral attachment protein that facilitates virus uptake by the infected cell, and is the target of the host humoral immune response to infection. The extracellular domain of this glycoprotein has N- glycosylation sequons at Asn37, Asn247, and Asn319. Appropriate glycosylation of these sequons is important in the expression of the glycoprotein. Soluble forms of rabies virus glycoprotein were constructed by insertion of a stop codon just external to the transmembrane domain. Using site-directed mutagenesis and expression in transfected eukaryotic cells, it was possible to compare the effects of site-specific glycosylation on the cell-surface expression and secretion of transmembrane and soluble forms, respectively, of the same glycoprotein. These studies yielded the surprising finding that although any of the three sequons permitted cell surface expression of full-length rabies virus glycoprotein, only the N-glycan at Asn319 permitted secretion of soluble rabies virus glycoprotein. Despite its biological and medical importance, it has not yet been possible to determine the crystal structure of the full-length transmembrane form of rabies virus glycoprotein which contains heterogeneous oligosaccharides. The current studies demonstrate that a soluble form of rabies virus glycoprotein containing only one sequon at Asn319 is efficiently secreted in the presence of the N-glycan processing inhibitor 1-deoxymannojirimycin. Thus, it is possible to purify a conformationally relevant form of rabies virus glycoprotein that contains only one N-glycan with a substantial reduction in its microheterogeneity. This form of the glycoprotein may be particularly useful for future studies aimed at elucidating the three-dimensional structure of this important glycoprotein.      

Satiation amount, frequency of feeding and gastric emptying rate in Salmo gairdneri

Rainbow trout consumed food in direct proportion to their body weight although the ration increased with temperature. Satiation time varied as 0.031 weight+0.868 temperature+29.145 min. Appetite after deprivation returned in close conjunction with gastric emptying, as judged from serial slaughter studies. Trout trained to operate demand feeders ate less but exhibited feeding rhythms even under conditions of constant illumination. Radiography showed that these rhythms closely paralleled gastric emptying. When offered food diluted with kaolin, the fish compensated by eating more food. This was achieved by increasing feeding frequency caused by a more rapid rate of gastric emptying.     

Mycoflora and mycotoxins natural occurrence in corn from entre rios province, Argentina

Corn samples were collected in 1999 from three departments of Entre Réos province, Argentina, and were surveyed for mould contamination and natural occurrence ofFusarium mycotoxins, ochratoxin A and aflatoxins.Fusarium verticillioides was the most prevalent fungal species recorded at all departments. Zearalenone, deoxynivalenol and ochratoxin A were not found in any samples. Only one of the 52 corn samples analysed was contaminated with aflatoxin B₁ (17 μg/kg). Fumonisin B₁ was found in 58 % of samples (range of positive samples: 47– 3,347 μg/kg), fumonisin B₂ in 33.0 % (range of positive samples: 23–537 μg/kg) and fumonisin B₃ in 25.0 % (range of positive samples: 24–287 μg/kg) of them. This is the first report on the natural occurrence of mycotoxins in corn from Entre Ríos province, Argentina. Levels of fumonisins were lower than detected in other Argentinian provinces.