Biochemical and molecular biological characterization of a lipase produced by the fungus Rhizopus delemar

The results of a comprehensive biochemical and molecular biological investigation of the lipase produced by the mycelial fungus Rhizopus delemar are described. This enzyme cleaves and synthesizes primary esters and related bonds, exhibits 1,3-positional selectivity in its actions on glycerides, and is a member of a family of enzymes that have been widely used in applied biocatalysis. Use of glycerol as main carbon source rather than glucose or lipid supported mycelial growth and lipase production. The enzyme was purified to homogeneity and characterized. Pure lipase was crystallized and its three-dimensional structure determined. The enzyme was found to adopt a configuration similar to those of other members of its homologous family. The structural data also indicated that lipases possess greater configurational mobility than had been previously appreciated. A complementary DNA clone was isolated that contained the full length lipase gene. The nucleic acid sequence of this cDNA indicated that it was initially synthesized as a preproenzyme, and allowed determination of the complete predicted amino acid sequence of the lipase, and its comparison to the sequences of related enzymes. Truncated forms of the cloned cDNA were produced that encoded either mature or prepro-lipase. These DNAs were introduced into a tightly regulated E. coli expression system, overcoming the toxicity of the enzyme while also allowing overproduction of lipase. Molecular modelling was employed to guide the rational mutagenesis of the enzyme, identifying sites within the substrate binding region that regulated substrate selectivity. Mutant lipases were generated with altered substrate specificities, creating novel enzymes and beginning the definition of structure-function relationships in the lipolytic enzymes.     

Crystallization of hydroxybutyrate oligomers: 1. morphology and folding

Exact length hydroxybutyrate oligomers containing 24 and 32 repeat units have been prepared and their crystallization behaviour and crystal morphology observed.The oligomers form crystals from dilute solution and from the melt that have similar overall morphologies to crystals of the polymer, poly(hydroxybutyrate). Electron diffraction indicates that the chains are closely perpendicular to the basal planes of the crystals.Wide angle X-ray diffraction suggests that all crystals, no matter what their thickness, have a high degree of crystallinity and the same crystal structure.The crystals have a range of thicknesses, as measured by small angle X-ray diffraction. The most common thicknesses correspond to the extended stem length and to one half or, surprisingly, two thirds of that value. A model is proposed for the non-integer fraction crystals in which half of the chain ends are incorporated in the crystals themselves.     

Ethanol reforming and partial oxidation with Cu/Nb2O5 catalyst

Ethanol reforming and partial oxidation were studied on Cu/Nb₂O₅ and Ni/Al₂O₃ catalysts. Compared to the Ni/Al₂O₃ catalyst, the Cu/Nb₂O₅ catalyst presents conversion as high as Ni/Al₂O₃ catalyst, however, for the same level of formation of hydrogen it occurs at much lower temperature on the Cu/Nb₂O₅ catalyst, 200 °C lower than for the Ni/Al₂O₃ catalyst, with remarkable little formation of CO, which can be attributed to the strong interaction between copper and niobia. Temperature-programmed desorption (TPD-ethanol) and surface reactions (TPSR) of partial oxidation of ethanol showed formation of ethylene, acetaldehyde, ethane and mainly H₂ and CO₂ besides little methane. DRIFTS results are in accordance with TPD analysis and the formation of acetate species at room temperature suggests reactivity of the surface and its oxidative dehydrogenation capacity. The adsorption of ethanol gives rise to ethoxide species, which form acetate and acetaldehyde that can be oxidized to CO₂ via carbonate. A comparison with reported results for Cu/Al₂O₃ this catalyst is promising, yielding high level of H₂ with little CO production during reforming and partial oxidation reaction. The maximum H₂ formation for the partial oxidation of ethanol was 41% at ratio (O₂/Et) 0.8, increasing to 50% at ratio 1.5. The H₂/CO is around 10 for the partial oxidation and 7 for steam reforming, which is excellent, compared to the Ni/Al₂O₃ catalyst with a factor 4–8 lower.     

Expansion and shrinkage of oversulphated portland cements

Expansion and shrinkage tests on mortars made from a range of cements with SO₃ contents in excess of the limits specified in BS 12 are described. The mortar specimens were cured under water from 24 hours to 7 days and then dried at 65% RH and 20°C. It is shown that there is a small range of SO₃ contents within which sharp increases in 7 day expansion occur ranging from 80 to 170 micro-strain/SO₃% and that within this small range of SO₃ contents the subsequent drying shrinkage is not adversely affected.     

Memory and aging: The role of retrieval processes.

A review of the literature demonstrates that production deficiency hypotheses are unable to account fully for the fact that older adults perform more poorly on memory tasks than young adults. The possibility is explored that age-related differences are due to changes in fundamental processes involved in retrieval of information from memory, namely, (a) utilization of contextual information and (b) activation processes occurring in semantic memory. Automatic as well as intentional processes are examined. (5? p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Novel Processing Route to Control Grain Growth in Submicrometer Alumina Compacts

A novel processing procedure for significantly suppressing grain growth in submicrometer alumina compacts has been developed and implemented with the intent of ultimately using the same processing route to control grain size in nanophase alumina compacts. In this study, partially sintered alumina pellets made from 0.5 µm starting powders are altered by the chemical infiltration of Si₃N₄. The control and infiltrated pellets are then heated to 1650°C for 4 h. The fully sintered pellets are approximately 97% dense. Suppressed grain growth is observed in the infiltrated pellets. The average grain size in the control pellets after densification is 4.2 and 1.2 µm in the infiltrated pellets. Depth of infiltration is measured using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Depending on the specific infiltration conditions used, the outer 15-50% of the infiltrated pellets exhibit a graded microstructure consisting of a region of abnormal grain growth and a region of suppressed grain growth. Abnormal grain growth is visible on the outer surfaces of the infiltrated pellets where a relatively high ratio of Si to N is present. Further into the pellet, after some depletion of the Si source gas has occurred, regions of suppressed grain growth are apparent. Based on these results, an infiltration profile is determined. A mathematical model is developed to describe the infiltration process and to determine optimal infiltration conditions. High-resolution electron microscopy (HREM), energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and X-ray photoelectron spectroscopy (XPS) are used to study the infiltrated samples.     

High speed power

This paper presents the need for compatibility between European rail networks. This leads to the adoption of dual 25 kV as the power of choice for operators. Dual 25 kV literally doubles the power available to rail networks, helping rail operators to meet some of the demands they are facing. Not surprisingly, this fact, along with the EU directive on 'interoperability of the trans-European high speed rail system', which aims to ease the circulation of high-speed trains through the various train networks of the European Union, will lead it to become the future standard across Europe     

Effect of voluntary repetitive long-lasting muscle contraction activity on the BOLD signal as assessed by optimal hemodynamic response function

Objective

Among other neuroimaging techniques, functional magnetic resonance imaging (fMRI) can be useful for studying the development of motor fatigue. The aim of this study was to identify differences in cortical neuronal activation in nine subjects on three motor tasks: right-hand movement with minimum, maximum, and post-fatigue maximum finger flexion.

Materials and methods

fMRI activation maps for each subject and during each condition were obtained by estimating the optimal model of the hemodynamic response function (HRF) out of four standard HRF models and an individual-based HRF model (ibHRF).

Results

ibHRF was selected as the optimal model in six out of nine subjects for minimum movement, in five out of nine for maximum movement, and in eight out of nine for post-fatigue maximum movement. As compared to maximum movement, a large reduction in the total number of active voxels (primary sensorimotor area, supplementary motor area and cerebellum) was observed in post-fatigue maximum movement.

Conclusion

This is the first approach to the evaluation of long-lasting contraction effort in healthy subjects by means of the fMRI paradigm with the use of an individual-based hemodynamic response. The results may be relevant for defining a baseline in future studies on central fatigue in patients with neuropathological disorders.