β-Xylosidases from filamentous fungi: an overview

β-Xylosidases are hydrolytic enzymes which play an important role in xylan degradation, hydrolyzing xylobiose and xylooligosaccharides to xylose from the non-reducing end. Filamentous fungi are particularly interesting producers of this enzyme from an industrial point of view, due to the fact that they secrete β-xylosidases into the medium. Besides, fungal β-xylosidases are highly advantageous for their elevated activity levels and specificity. Interest in xylanolytic enzymes has been increasing, for their possible application in many biotechnological processes. This fact has driven the isolation, purification and characterization of several β-xylosidases. In this review, the mechanisms of action, substrate specificities, physicochemical characteristics, regulation at molecular level, molecular cloning and classification of filamentous fungal β-xylosidases are described. The potential industrial applications of fungal β-xylosidases will also be presented.     

Expression of the α-thionin gene from barley in tobacco confers enhanced resistance to bacterial pathogens

Thionins are cysteine-rich, 5 kDa polypeptides which are toxic to plant pathogens in vitro. Expression of the gene encoding α-thionin from barley endosperm, under the 35S promoter from cauliflower mosaic virus, conferred to transgenic tobacco enhanced resistance to the bacterial plant pathogens Pseudomonas syringae pv. tabaci 153 and P. syringae pv. syringae. The barley α-thionin gene, which has two introns, was correctly spliced in tobacco. The α-thionin in transgenic plants had the expected mobility in the gradient, when separated by high-performance liquid chromatography, reacted with monospecific antibodies and showed the expected antibiotic properties in vitro.     

Blood lactic acid level changes during acidosis induced by hydrochloric acid perfusion]

An increase in H+ ions concentration by infusion of hydrochloric acid produces a reduction in lactacidemia. This phenomenon is a result of the inhibitory effect of acidosis on phosphofructokinase producing a diminution of intracellular glycolysis.     

Kinetic study of the transient phase of a chemical reaction system coupled to an enzymatically catalyzed step. Application to the oxidation of epinine by tyrosinase

The present work deals with epinine oxidation by mushroom tyrosinase and sodium metaperiodate. Intermediates produced within short reaction times were characterized by repetitive scanning spectrophotometry and the stoichiometry of the appearance of the respective aminochrome was established. The oxidation pathway from epinine to aminochrome had the following steps: epinine----o-quinone-H+----o-quinone----leukoaminochrome----aminoc hrome. The stoichiometry for the conversion of o-quinone-H+ into the aminochrome of epinine followed the equation: 2 o-quinone-H+----epinine+aminochrome. A transient phase kinetic study has been developed for the system of chemical reactions coupled to an enzymatically catalyzed step, these taking place when epinine is oxidized by mushroom tyrosinase. Rate constants for the implied chemical steps at different temperature and pH values were calculated from analysis of the progress curves of aminochrome accumulation with time. The thermodynamic activation parameters of the chemical steps were also calculated.     

Seasonal diet by a generalist raptor: the case of the variable hawk (Geranoaetus polyosoma) at Atacama Desert,northern Chile

We determined the seasonal diet of the variable hawk, Geranoaetus polyosoma, in a hyperarid and threatened habitat in the Atacama Desert, northern Chile, by analysing the contents of the bird's pellets. We estimated the biomass and number of individuals of each prey species consumed. We compared our results with those of other studies on G. polyosoma in South America. In general, the diet was characterised by extremely low number of prey, low diversity of species consumed and high dietary breadth. In contrast with other biomes of Chile, in our study reptiles formed the dominant food item and accounted for the highest percentage of biomass consumed from autumn to spring, with rodents being a seasonally significant major food item. Arthropods were also consumed, but the biomass ingested was negligible. Statistically significant differences were noted across seasons in the prey items consumed, reflecting a flexible and opportunistic response to the scarcity of prey available. Our findings add to the data present on the basic natural history of G. polyosoma and can aid in its conservation in the Atacama Desert.     

Current status of IMRT in head and neck cancer

Background

IMRT provides highly conformal dose distributions creating non uniform spatial intensity using different segments in the beam.

Material & Methods and Results

Different retrospective studies have shown a high capability of IMRT to treat tumours close to the base of skull. Prospective studies have shown a decrease in xerostomia compared with conventional 3D conformal treatment (3DCRT). Modulation of intensity is performed by the movement of the multileaf collimator (MLC) that can deliver the radiation in different ways, such as static field segments, dynamic field segments and rotational delivery (arc therapy and tomotherapy). There are slight differences among the different techniques in terms of homogeneity, dose conformity and treatment delivery time.

Conclusions

The best method to deliver IMRT will depend on multiple factors such as deliverability, practicality, user training and plan quality.