Reaction Engineering Aspects of α-l,4-D-Glucan Phosphorylase Catalysis

Some important process properties of α-l,4-D-ghican phosphorylases isolated from the bacteriumCorynebacterium callunae and potato tubers (Solatium tuberosum) were compared. Apart from minor differences in their stability and specificity (represented by the maximum degree of maltodextrin conversion) and a 10-fold higher affinity of the plant phosphorylase for maltodextrin (K _M of 1.3 g/L at 300 mM of orthophosphate), the performances of both enzymes in a continuous ultrafiltration membrane reactor were almost identical. Product synthesis was carried out over a time course of 300–400 h in the presence or absence of auxiliary pullulanase (increasing the accessibility of the glucan substrate for phosphorolytic attack up to 15–20%). The effect of varied dilution rate and reaction temperature on the resulting productivities was quantitated, and a maximum operational temperature of 40°C was identified.     

Purification and characterization of a laccase from the white-rot fungus Trametes multicolor

The wood-degrading fungus Trametes multicolor secretes several laccase isoforms when grown on a simple medium containing copper in the millimolar range for stimulating laccase synthesis. The main isoenzyme laccase II was purified to apparent homogeneity from the culture supernatant by using anion-exchange chromatography and gel filtration. Laccase II is a monomeric glycoprotein with a molecular mass of 63 kDa as determined by sodium dodecylsulfate polyacrylamide gel electrophoresis, contains 18% glycosylation, and has a pI of 3.0. It oxidizes a variety of phenolic substrates as well as ferrocyanide and iodide. The pH optimum depends on the substrate employed and shows a bell-shaped pH activity profile with an optimum of 4.0 to 5.0 for the phenolic substrates, while the nonphenolic substrates ferrocyanide and 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonate) show a monotonic pH profile with a rate decreasing with increasing pH.     

Semi-wet growth and characterization of multi-functional nano-engineered mixed metal oxides for industrial application

This review paper covers the low temperature wet growth of nano-engineered particles of ZnO-based mixed metal oxides, their growth mechanism, and characterization using X-ray diffraction, SEM, TEM and IR, UV–visible, and XPS spectral techniques. Main focus of this article is centered on low temperature semi-wet methods of synthesis that are suitable for large scale production of zinc oxide-based systems mixed with iron oxide, copper oxide, nickel oxide and cobalt oxide. These mixed metal oxides have broad industrial applications as catalyst, semiconductors, adsorbents, superconductors, electro-ceramics, and antifungal agents in addition to extensive applications in medicines. This paper discusses the low-cost and environment friendly synthesis of these mixed metal oxides, measurement of properties and applicability of these materials systems.     

Spherically symmetric inhomogeneous dust collapse in higher dimensional space-time and cosmic censorship hypothesis

We consider a collapsing spherically symmetric inhomogeneous dust cloud in higher dimensional space-time. We show that the central singularity of collapse can be a strong curvature or a weak curvature naked singularity depending on the initial density distribution.     

Synaptic depression and short-term habituation are located in the sensory part of the mammalian startle pathway

Background  

Short-term habituation of the startle response represents an elementary form of learning in mammals. The underlying mechanism is located within the primary startle pathway, presumably at sensory synapses on giant neurons in the caudal pontine reticular nucleus (PnC). Short trains of action potentials in sensory afferent fibers induce depression of synaptic responses in PnC giant neurons, a phenomenon that has been proposed to be the cellular correlate for short-term habituation. We address here the question whether both this synaptic depression and the short-term habituation of the startle response are localized at the presynaptic terminals of sensory afferents. If this is confirmed, it would imply that these processes take place prior to multimodal signal integration, rather than occurring at postsynaptic sites on PnC giant neurons that directly drive motor neurons.     

Production of Hemicellulose- and Cellulose-Degrading enzymes by various strains ofSclerotium Rolfsii

A number of wild-type isolates ofSclerotium rolfsii were screened for their capacity to produce lignocellulolytic enzymes when grown on a cellulose-based medium.S. rolfsii proved to be an efficient producer of hemicellulolytic enzymes under the conditions selected for this screening, although there was a great variability in enzyme activities formed by the different isolates. In addition to xylanase and mannanase, which were produced in remarkably high levels, a number of accessory enzymes, which are important for the complete degradation of substituted hemicelluloses and include a-arabinosidase, acetyl esterase, and a-galactosidase, are formed byS. rolfsii. Efficient production of xylanase and mannanase was achieved when cellulose-based media were used for growth. Under these conditions, enhanced levels of endoglucanase were formed as well. Formation of xylanase and mannanase could be more specifically induced when using xylan or mannan as growth substrates, although the enzyme activities thus obtained were significantly lower compared to cultivations on cellulose as main inducing substrate.

     

Estimation of trace elements in some medicinal plants used in anti‐cancer drugs by PIXE

A trace elemental analysis was carried out in various parts of 12 anticancer medicinal plants, using the PIXE (particle‐induced X‐ray emission) technique. A 3‐MeV proton beam was used to excite the samples, and spectra were recorded using a Si (Li) detector. Data analysis was done using the GUPIX software. The elements Cl, K, Ca, Ti, V, Mn, Fe, Ni, Cu, Zn, Br and Sr were identified, and their concentrations estimated. The results of the present study provide justification for the usage of these medicinal plants in the development of anticancer drugs. Copyright © 2012 John Wiley & Sons, Ltd.     

Production of a novel pyranose 2-0xidase by basidiomyceteTrametes multicolor

During a screening for the enzyme pyranose 2-oxidase (P2O) which has a great potential as a biocatalyst for carbohydrate transformations, Trametes multicolor was identified as a promising, not-yet-described producer of this particular enzyme activity. Furthermore, it was found in this screening that the enzyme frequently occurs in basidiomycetes. Intracellular P2O was produced in a growth-associated manner by T. multicolor during growth on various substrates, including mono-, oligo-, and polysaccharides. Highest levels of this enzyme activity were formed when lactose or whey were used as substrates. Peptones from casein and other casein hydrolysates were found to be the most favorable nitrogen sources for the formation of P2O. By applying an appropriate feeding strategy for the substrate lactose, which ensured an elevated concentration of the carbon source during the entire cultivation, levels of P2O activity obtained in laboratory fermentations, as well as the productivity of these bioprocess experiments, could be enhanced more than 2.5-fold.     

Enzymatic Synthesis of α-Glucose-1-phosphate: A Study Employing a New α-1,4 Glucan Phosphorylase from Corynebacterium callunae 1

Abstract

In synthetic pathways to complex carbohydrates such as oligosaccharides or nucleotide sugars the activated sugar 1-phosphates serve as important starting molecules. In this study the enzymatic synthesis of α-glucose-1-phosphate (Glc-1-P) has been investigated using a new bacterial α-glucan phosphorylase from Corynebacterium callunae. The major factors governing the rate of reaction and the attainable degree of substrate conversion have been identified and, accordingly, for optimizing the yield and limiting reaction time for the enzymatic process several points must be considered: (i) the pH-dependent equilibrium of reaction, (ii) product inhibition of the phosphorylase and (iii) enzymatic cleavage of α-1,6 glycosidic linkages present in α-1,4-glucans such as starch or maltodextrins by pullulanases to improve their phosphorolytic conversion. Results obtained in continuous experiments with the phosphorylase retained in an ultrafiltration membrane reactor confirmed the complete operational stability of the enzyme for several days at 30 °C. Since no more than approximately 18 % of the inorganic phosphate can be converted into Glc-1-P an efficient procedure for phosphate and product recovery will be particularly important.