β-Glucosidase from the cellulolytic system of Alternaria alternata autolyzed cultures

Abstract A β-glucosidase from centrifugated autolyzed cultures of Alternaria alternata has been purified 71 times by Sephadex G-200, CM-Biogel A and DEAE-Biogel A successively. The enzyme is a glycoprotein with 16% sugar and a M _r of 160 000, formed by two subunits of 60 000 and 80 000. The enzyme has optimum pH of 5 units and optimum reaction temperature of 50°C, being stable in a pH range of 3–8 and 0 to 60°C. The enzyme hydrolyzes different substrates showing maximum affinity and maximum hydrolysis velocity on cellobiose. The β-glucosidase is inhibited by gluconolactone but not by 10 mM glucose.     

Antigenic determinants expressed by human C4 allotypes; a study of 325 families provides evidence for the structural antigenic model

The antigenic determinants of human C4 have been defined by human IgG antisera, Rodgers (Rg) and Chido (Ch), in hemagglutination-inhibition assays (HAI). Eight (2 Rg and 6 Ch) are of high frequency, > 90% , and 1, WH, is of low frequency, 15 %. The phenotypic combinations are complex; generally, C4A expresses Rg, and C4B has Ch, but reverse antigenicities have been established both by HAI and by sequence data of selected C4 allotypes. A study of 325 families provides data on the antigenic expression of each C4 allotype and demonstrates strong associations. A structural model for the antigenic determinants of C4 proteins has been proposed and is completely supported by the family material. Of the 16 possible antigenic combinations for C4 proteins, only 3 are undetected. A new Ch combination has been recorded in two French families. The reported sequence variation within the C4d region can account for the antigenic determinants but leaves the location of electrophoretic variation in C4 still unclear.     

Chromium in plants

Chromium is an essential trace element and is associated with some biological pathways, especially with glucose tolerance. For these reasons, we decided to determine the concentration of chromium in two sets of Brazilian medicinal plants. The first group consisted of plants that are considered as antidiabetic, whereas the second included plants that do not have this therapeutic property. The concentration of chromium was determined by flameless atomic absorption. All the plants analyzed contain chromium in the normal range for this element, but the hypoglycemic plants contain more chromium than the others (1–4 μg/g compared to 0.5–1.5 μg/g).     

High Ammonia Levels in Brain Induce Tubulin in Cerebrum but Not in Cerebellum

Ingestion of large amounts of ammonium increases markedly the content of tubulin in brain. The effect on tubulin induction of ammonium ingestion for up to 100 days was investigated. Brain tubulin content showed a rapid initial increase (28%) at 2 days and reached 50% after 100 days on the diet. To discern if ammonia, the increase in urea synthesis, or both was responsible for tubulin induction, rats were maintained at several levels of uremia (by administering diets containing 0 to 80% protein) or in hyperammonemia (by urease treatment). Only ammonium administration in the diet and urease injection induced tubulin in brain. Tubulin was quantified in three different brain regions. There was a regional selectivity of tubulin induction by ammonia in rat brain. Whereas the cerebellum remained unaltered, the paleencephalon showed the highest increase, and the cerebral cortex exhibited only a modest increase.     

Characterization of genetic transformation in Streptococcus oralis NCTC 11427: Expression of the pneumococcal amidase in S. oralis using a new shuttle vector

Summary We have worked out conditions for the study of competence development and genetic transformation in Streptococcus oralis NCTC 11427 (type strain), a species that contains choline in the cell wall. The peak of competence was found at the early exponential phase of growth and the optimal conditions for transformation were achieved with shuttle plasmids prepared from S. pneumoniae or from Escherichia coli serving as donor DNA. Transformation with dye-bouyant density gradient purified plasmid preparations followed first-order kinetics. The pneumococcal amidase can be expressed in S. oralis harbouring a plasmid carrying the lytA gene. This enzyme lysed the cell wall of the transformed cell in the presence of detergents.     

Ultrastructure of the mitotic nuclei in Leishmania mexicana ssp. Tridimensional reconstruction of the mitotic spindle and dense plaques

The ultrastructure of mitotic nuclei of the promastigote Leishmania mexicana ssp. was studied by serial thin sections and three-dimensional reconstructions of each divisional stage. At the beginning of nuclear division (equatorial stage), a set of six dense plaques located about the equatorial region of the nucleus and a microtubular spindle develops in the two opposing poles of the nucleus (two sets of polar microtubules). The microtubular mitotic spindle is entirely intranuclear with the nuclear membrane persisting through mitosis. The polar spindle consists of a discrete bundle of about 50 microtubules and the equatorial spindle is formed by about 100 microtubules. The spindle may contain several continuous microtubules, but no microtubular organizing centres were observed in association with the spindle. The plaques and hemiplaques are associated with microtubular bundles; some of the spindle microtubules converge on kinetochore-like plaques. It is suggested that the spindle has a special significance in the physiology of mitosis. The two sets of hemiplaques may guide the separation of the daughter genomes. At the beginning of the elongational stage the mitotic plaques split into halves and each set of half-plaques migrates to one pole. It is concluded that the dense plaques play a kinetochore-like role and thus Leishmania mexicana ssp. may have six chromosomal units. Mitotic events of this species are essentially similar to those of Trypanosoma cruzi.     

Activation of Ca2+-dependent processes during heat shock: role in cell thermoresistance

In this brief review, it is proposed that some Ca2+-dependent processes are induced upon subjecting cells to hyperthermic temperature, and play an essential role in the final cell responses. The triggering signal does not involve external Ca2+. Instead, it is most likely to be generated by a redistribution of Ca2+ between the internal pools. A role for heat-induced Ca2+-dependent processes is supported by findings that Ca2+-active agents such as chelators, ionophores, or anticalmodulin drugs modify the cytotoxic action of hyperthermia and that some heat shock proteins are calmodulin-binding proteins. Furthermore, within minutes at hyperthermic temperature, changes are observed in the pattern of phosphoproteins suggesting that heat shock activates kinase or phosphatase activities, processes which are often mediated by Ca2+. Suggestive evidence that these phosphorylation events are determinants of cell thermoresistance is provided by the fact that one of these proteins whose phosphorylation changes rapidly upon hyperthermia is a heat shock protein (HSP28) and that the content of HSP28 is elevated not only in thermotolerant cells but also in a family of thermoresistant variants isolated after mutagenesis of Chinese hamster cells.     

Extramacrochaetae,a trans-acting gene of the achaete-scute complex of Drosophila involved in cell communication

Summary Phenotypic analyses of genetic combinations involving the gene extramacrochaetae (emc) reveal its participation in the differentiation of both sensory elements and wing veins. The study of near-amorphic alleles of emc in mitotitc recombination clones indicates that it also affects cell proliferation. These clones show abnormal sizes, shapes and spatial distribution. They differentiate extra sensory elements as well as extra veins. A gain of function mutation in the gene causes opposite phenotypes in both differentiation systems. The effects of the mutant on proliferation and patterning are consistent with the emc gene being involved in the transfer of information between neighbouring cells, which leads to the spatial expression of the achaetescute gene complex and genes involved in vein formation.     

Experimental aflatoxin production in Manchego-type cheese

Manchego-type cheese, a typical Spanish cheese, was inoculated in various ways with an aflatoxigenic organism, Aspergillus parasiticus NRRL 2999, to study the production of aflatoxin. When the original milk was contaminated with a spore suspension, aflatoxin was not detected in paraffin-covered cheeses although it was present in the top layer of non-paraffin-covered cheeses after ripening at 15°C for 60 d. When the cheese surface was inoculated, no aflatoxins were detected in paraffin-covered cheeses after ripening for 60 d although they were found when the cheeses were ripened for 30 d. In non-paraffin-covered cheeses aflatoxins were detected only in the top layer and in the second 10 mm layer when cheeses were incubated after the normal ripening at 28°C for 30 d. When the centre of the cheese was inoculated, no aflatoxins were detected although Aspergillus grew slightly along the inoculation area. When cheese portions were inoculated, fungal growth was evident after incubation at 28° and 15°C for 6 d but there was no growth at 10°C after 50 d. At 28°C aflatoxins were detected at a concentration of 132 μg/g after 13 d, the highest level obtained. In cheese paste at 28° and 15°C, growth was intense, but the level of aflatoxins detected was lower than in cheese portions. At 10°C the growth was heavy, but aflatoxins were not detected.