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.     

Molecular recognition of anions by synthetic receptors

Over the past year, several significant developments have been made in the field of anion binding. The fundamental principles of molecular recognition are increasingly being better understood, and of particular interest are reports of several synthetic anion receptors able to perform their task in complex natural media. Additionally, macroscopic devices such as anion specific electrodes and membranes based on a molecular recognition approach are now being made.     

The position of the epistatic S locus in the halothane linkage group in pigs

The linkage of the Phi, Pgd, Po2, S, H and halothane sensitivity loci was followed in a Belgian Landrace family, heterozygous for these systems over 6 generations. Recombination next to the S locus occurred mainly in pigs belonging to this particular family. From this investigation the position of the S locus is proved to be outwith the Phi-Pgd region, next to Phi . Therefore the gene sequence S - Phi - Hal -H- Po2 -Pgd is proposed. Higher recombination rates were observed in the female parental line of the multiheterozygous family when compared to the male parental line. Additional data from animals, unrelated to this strain, confirm the evidence of close linkage of the S system to the nearest marker loci.     

Isoquinoline alkaloids from cell suspension cultures of Fumaria capreolata

Fumaria capreolata was taken into cell suspension culture. The culture yielded a biomass of about 12 g dry weight per liter of medium; the dried cells contained ca. 0.1% of alkaloids. Besides choline, the following ten known isoquinoline alkaloids were isolated from the cell extract in crystalline form: coptisine, dehydrocheilanthifoline; (+)-isoboldine; magnoflorine; N-methylcoclaurine; (+)-reticuline; (–)-pallidine; protopine; sanguinarine; (–)-scoulerine. This is the most diverse isoquinoline alkaloid spectrum thus far published for a cell suspension culture.     

Effects of EEG of the osmotic opening of the blood-brain barrier in rats

EEG activity was recorded in rats submitted to osmotic opening of the BBB by intracarotid mannitol infusion.This procedure produced an immediate short-lasting depression of the EEG and a tardive paroxysmal EEG activity. Both these phenomena were more relevant on the ipsilateral hemisphere. In some instances a tonico-clonic seizure was recorded.Pre-treatment with diazepam abolished the occurrence of the tardive EEG and behavioral modifications.In accord with previous findings, focal seizure activity is likely to be responsible for the metabolic abnormalities associated with osmotic opening of the BBB. This preparation therefore produces in the brain unphysiological states in respect to local metabolism and electrical function.     

Structure–antimicrobial activity of some natural isocoumarins and their analogues

Three naturally occurring isocoumarins (paepalantine, paepalantine 9-O-beta-D-glucopyranoside and paepalantine 9-O-beta-D-allopyranosyl(1 --> 6) glucopyranoside) and two semi-synthetic analogues, 9,10-acylated compound and 9-OH-10-methylated compound, structurally similar to paepalantine, were evaluated for antimicrobial activity using a spectrophotometric microdilution technique. The paepalantine was active against S. aureus, S. epidermidis, and E. faecalis while the other four compounds proved ineffective against all microorganisms tested at concentrations of 500 microg/ml. Variations in phenolic substitution at OH-9 and/or OH-10 in the paepalantine molecule resulted in compounds without antimicrobial activity. A combination of structural features, two phenolic groups as cathecolic system, forms an oxygenated system arrangement that may reflect the potentially antimicrobial properties of paepalantine.     

Repair mechanisms involved in muscle regeneration following partial excision of the rat gastrocnemius muscle

The sequential cytological events of the regeneration process, after partial excision of the gastrocnemius muscle in the rat, were followed by light and electron microscopy. During the first 2 days after injury leukocytes and macrophages infiltrate into the traumatized area. Myogenic regeneration is then characterized by mainly two repair mechanisms. Mononucleated cells, that populate the excised area, most probably fuse together to give rise to newly formed multinucleated myotubes that further develop to striated myofibers. Another mechanism involves the repair of injured muscle fibers by the possible fusion of mononucleated cells with their necrotic cut ends. Consequently, by addition of nuclei and new muscular material, sarcoplasmic outgrowths from the injured fibers are formed. It is concluded that mainly two repair mechanisms are involved in the regeneration process following partial excision of a muscle: addition of new muscle fibers in a process similar to that of embryonic myogenesis and also meristic growth from the injured fibers.     

Penetration of analogues of H2O and CO2 in proteins studied by room temperature phosphorescence of tryptophan.

The influence of the protein matrix on the reactivity of external molecules with a species buried within the protein interior is considered in two general ways: (1) there may be structural fluctuations that allow for the diffusive penetration of the small molecules and/or (2) the external molecule may react over a distance. As a means to study the protein matrix, a reactive species within the protein can be formed by exciting tryptophan to the triplet state, and then the reaction of the triplet-state molecule with an external molecule can be monitored by a decrease in phosphorescence. In this work, the quenching ability (i.e., reactivity) was examined for H2S, CS2, and NO2- acting on tryptophan phosphorescence in parvalbumin, azurin, horse liver alcohol dehydrogenase, and alkaline phosphatase. A comparison of charged versus uncharged quenchers (H2S vs SH- and CS2 vs NO2-) reveals that the uncharged molecules are much more effective than charged species in quenching the phosphorescence of fully buried tryptophan, whereas the quenching for exposed tryptophan is relatively independent of the charge of the quencher. This is consistent with the view that uncharged triatomic molecules can penetrate the protein matrix to some extent. The energies of activation of the quenching reaction are low for the charged quenchers and higher for the uncharged CS2. A model is presented in which the quenchability of a buried tryptophan is inversely related to the distance from the surface when diffusion through the protein is the rate-limiting step.(ABSTRACT TRUNCATED AT 250 WORDS)