Quantitative enzymatic production of 1,6-diacyl sorbitol esters

The enzymatic synthesis of several sorbitol diesters whose HLB values are similar to those of monoglycerides (the largest single type of food-grade emulsifiers) has been studied. The procedure is carried out by the simple addition of the polyol to a solution of the fatty acid and is based on continuous precipitation of the diester formed at a low temperature. A solvent of relatively low toxicity (acetone) was used. Pure fatty acids of different chain lengths (lauric and caprylic acids) were employed. The procedure was also tested using the acids obtained from total hydrolysis of olive oil, as an example of industrial feedstocks of fatty acids. This synthesis strategy gave complete conversion of sorbitol and >95% yields of the corresponding 1,6-diesters. In addition, a strategy to reduce the reaction time is reported. The enzymatic procedure permits minimization of the solvent/sugar ratio because it does not require complete dissolution of the sugar in the organic solvent. Copyright 1998 John Wiley & Sons, Inc.     

Solution conformation and dynamics of a fungal cell wall polysaccharide isolated from Microsporum gypseum

The conformational and dynamical features of a branched mannan isolated from a fungal cell wall have been analysed by homo and heteronuclear NMR methods, employing different magnetic fields. 1HNMR cross relaxation times have been obtained for this polysaccharide and have been interpreted qualitatively using different motional models. 13C NMR relaxation parameters (T1, T2, NOE) have also been measured and interpreted using different approximations based on the Lipari and Szabo model free approach. The analysis of the data indicate the existence of important flexibility for the different linkages of the polysaccharide. Motions in the range of 4–6 ns contribute to the relaxation of the macromolecule, although faster internal motions in the 500 ps and 100 ps timescales are also present. These time scales indicate that segmental motions as well as internal motions around the glycosidic linkages are the major sources of relaxation for this molecule at 318 K. Molecular dynamics simulations have also been performed. The obtained results also indicate that the polysaccharide possess a substantial amount of conformational freedom.     

Tree Ferns in the Interior and at the Edge of a Mexican Cloud Forest Remnant: Spore Germination and Sporophyte Survival and Establishment1

The three most common tree fern species in a Mexican montane cloud forest fragment (Alsophila firma, Lophosoria quadripinnata and Sphaeropteris horrida) were selected for laboratory and transplant experiments. The objectives were: (1) to determine the percentage of spore germination and gametophytes producing sporophytes, and (2) to compare early establishment of sporophytes at the edge and in the interior of the forest. Percent spore germination varied between 16 and 86 percent, and the number of gametophytes that produced sporophytes was high (>50%). Survival and growth of sporophytes differed between species and habitats. Survival was greater at the edge than in the forest interior for Lophosoria, but it was similar for Alsophila and Sphaeropteris. Number and length of fronds were higher at the forest edge for individuals of Alsophila and Lophosoria, but not for Sphaeropteris. RGR was higher at the forest edge than in the forest interior for sporophytes of the three species. This study suggests that the forest edge is an appropriate habitat for establishment of Alsophila and Lophosoria, but Sphaeropteris is apparently a forest interior species.     

Composition of the cell wall polysaccharides in some geophilic dermatophytes

The main polysaccharide fractions from cell wall material of several geophilic dermatophyte species were characterized as a glucomannan (F1S) which amounted to 4.0–6.5% and a glucan-chitin complex representing 44.2–71.0%. The neutral sugar content of fraction F1S in these species was mannose (38.7–78.2%), galactose (0.3–7.3%) and glucose (3.2–8.2%) except inM. fulvum (21.9%) andE. stockdaleae (12.5%). Small proportions of xylose, about 1%, were found in this fraction except inM. fulvum which reached 7.8% and inM. nanum which lacked xylose. The main products detected after Smith degradation were glycerol and glucose. From fraction F1S ofM. fulvum a glucan (18.3%) and a mannan (41.5%) were obtained. These two polysaccharides could be used as chemotaxonomic characters for the definition of this group of fungi.     

Discs large (Dlg1) complexes in lymphocyte activation

T cell antigen recognition involves the formation of a structured interface between antigen-presenting and T cells that facilitates the specific transmission of activating and desensitizing stimuli. The molecular machinery that organizes the signaling molecules and controls their disposition in response to activation remains poorly understood. We show here that in T cells Discs large (Dlg1), a PDZ domain-containing protein, is recruited upon activation to cortical actin and forms complexes with early participants in T cell activation. Transient overexpression of Dlg1 attenuates basal and Vav1-induced NFAT reporter activation. Reduction of Dlg1 expression by RNA interference enhances both CD3- and superantigen-mediated NFAT activation. Attenuation of antigen receptor signaling appears to be a complex, highly orchestrated event that involves the mutual segregation of important elements of the early signaling complex.     

Composition and capacity of Institutional Review Boards,and challenges experienced by members in ethics review processes in Addis Ababa,Ethiopia: An exploratory qualitative study

Few studies in sub-Saharan Africa evaluate Institutional Review Boards (IRBs) capacity. The study aims to explore the composition of IRBs, training, and challenges experienced in the ethics review processes by members of research institutions and universities in Addis Ababa, Ethiopia. Our findings indicate that most IRBs members were trained on research ethics and good clinical practice. However, majority perceived the trainings as basic. IRB members faced several challenges including: investigators wanting rapid review; time pressure; investigators not following checklists; limited expertise in reviewing clinical trials, studies on genetics, and traditional medicine; lack of IRB offices for administrative work; competing tasks; limited staffing and the lack of a standardized review system. There is need for advanced training on research ethics to meet the evolving research needs. In addition, investments in IRBs are needed in terms of funding, and physical and human resources in Addis Ababa and Ethiopia in general.