Effect of primycin on some electric properties of the frog skeletal muscle

The effect of primycin, a guanidine-type antibiotic was studied on the electric properties and 42K+ uptake of the frog sartorius and semitendinosus muscle. Both in normal and choline chloride Ringer solution, primycin evoked a concentration and time dependent depolarization of the surface membrane of the muscle. This depolarization was significantly increased by Na ions. Primycin treatment was shown to evoke a dose-dependent decrease of the depolarization induced by 20 mM K+-Ringer. When the muscles were incubated in a Ringer solution containing choline chloride, during an incubation period of 30 min the uptake of 42K+ was decreased to 12% upon the exposure to 5 x 10(-6) mol primycin as compared to the control value. As the primycin-induced depolarization increased, the shape and amplitude of the action potentials elicited by square-wave electric impulses were altered and decreased, respectively. In sodium isaethionate Ringer 1--2 x 10(-6) M primycin induced a slow depolarization resulting in firing potentials. The results suggest that primycin depolarizes the surface membrane exclusively through the blockade of the resting K+ channels, the other phenomena being the results of this depolarizing effect.     

Some meteorological conditions associated with forest fires in Galicia (Spain)

The present paper offers data on the effect of certain meteorological parameters on the outbreak of forest fires in Galicia (Spain). In a day-to-day analysis, the values of the stability of the air column and the saturation deficit at the lower levels are related to the number of fires occurring in the following 24 h.     

Continuous-flow solid-phase synthesis of potential antigenic peptides of hepatitis B virus

The synthesis of three hepatitis B surface antigens derived from S and pre-S proteins (adw S(140-147), [Tyr148] adw S(139-148), and adw pre-S(120-145)) has been accomplished by the continuous flow Fmoc-polyamide solid phase method. The use of different scavengers and trimethylsilyl bromide (TMSBr) in trifluoroacetic acid as deprotecting procedures is discussed.     

Colonization and extinction of land planarians (Platyhelminthes,Tricladida) in a Brazilian Atlantic Forest regrowth remnant

Long-term assessments of species assemblages are valuable tools for detecting species ecological preferences and their dispersal tracks, as well as for assessing the possible effects of alien species on native communities. Here we report a 50-year-long study on population dynamics of the four species of land flatworms (Platyhelminthes, Tricladida, Terricola) that have colonized or become extinct in a 70-year-old Atlantic Forest regrowth remnant through the period 1955–2006. On the one hand, the two initially most abundant species, which are native to the study site, Notogynaphallia ernesti and Geoplana multicolor have declined over decades and at present do not exist in the forest remnant. The extinction of these species is most likely related with their preference for open vegetation areas, which presently do not exist in the forest remnant. On the other hand, the neotropical Geoplaninae 1 and the exotic Endeavouria septemlineata were detected in the forest only very recently. The long-term study allowed us to conclude that Geoplaninae 1 was introduced into the study area, although it is only known from the study site. Endeavouria septemlineata, an active predator of the exotic giant African snail, is originally known from Hawaii. This land flatworm species was observed repeatedly in Brazilian anthropogenic areas, and this is the first report of the species in relatively well preserved native forest, which may be evidence of an ongoing adaptive process. Monitoring of its geographic spread and its ecological role would be a good practice for preventing potential damaging effects, since it also feeds on native mollusk fauna, as we observed in lab conditions. Júlio Pedroni: Granted by CNPQ–Brazil.     

Identification of UDP-linked murein precursors as contaminants in recombinant proteins of low molecular weight.

The A(280)/A(260) ratio of a purified protein is frequently used as an indication of the purity of the preparation with respect to nucleic acids. We show here that for low-molecular-weight recombinant proteins purified from Escherichia coli, a low A(280)/A(260) ratio can also result from contamination with UDP-linked murein precursors derived from bacterial cell wall metabolism. Although these precursors are small molecules of molecular weight 1000-1200, they comigrate in gel filtration with recombinant human FKBP (MW 11,820). This gel filtration behavior, which is distinct from that of unmodified mononucleotides, does not reflect binding interactions with FKBP, but is an intrinsic property of these precursors. Therefore, these molecules would be expected to copurify with other low-molecular-weight proteins, especially in the abbreviated purification protocols made possible by freeze-thaw release of recombinant proteins from E. coli (Johnson, B. H., and Hecht, M. H. (1994) BioTechnology 12, 1357-1360). Several alternative strategies are discussed for integrating these findings into the design of improved purification procedures for low-molecular-weight recombinant proteins.     

Identification, sequencing and mutagenesis of the gene for a d-carbamoylase from Agrobacterium radiobacter

Abstract A clone positive for d-carbamoylase activity (2.7 kb Hin dIII- Bam H1 DNA fragment) was obtained by screening a genomic library of Agrobacterium radiobacter in Escherichia coli . This DNA fragment contains an open reading frame of 912 bp which is predicted to encode a peptide of 304 amino acids with a calculated molecular mass of 34247 Da. The d-carbamoylase gene. named cauA , was placed under the control of T7 RNA-dependent promoter and expressed in E. coli BL21 (DE3). After induction with isopropyl-thio-β-d-galactopyranoside, the synthesis of d-carbamoylase in E. coli reached about 40% of the total protein. The expressed protein was shown to possess a molecular mass, on SDS-PAGE, of 36 kDa and showed an enhanced allowed us to establish that a Pro¹⁴→Leu¹⁴ exchange leads to an inactive enzyme species, while a Cys²⁷⁹→Ser²⁷⁹ exchange did not impair the functional properties of the enxyme.     

Peroxisomes and peroxisomal enzymes along the crypt-villus axis of the rat intestine

Abstract. The development of peroxisomes and expression of their enzymes were investigated in differentiating intestinal epithelial cells during their migration along the crypt-villus axis. Sequential cell populations harvested by a low-temperature method were identified by microscopy, determination of alkaline phosphatase and sucrase activities and incorporation of [³H]-thymidine into DNA. Ultrastructural cytochemistry after staining for catalase activity, revealed the presence of peroxisomes in undifferentiated stem cells located in the crypt region. Morphometry indicated that the number of these organelles increased as intestinal epithelial cells differentiate. Catalase activity was higher in the crypt cells than in the mature enterocytes harvested from villus tips. On the other hand, an increasing gradient of activity was observed from crypts to villus tips for peroxisomal oxidases, i.e. fatty acyl coA oxidase, D-amino acid oxidase and polyamine oxidase. These findings indicate that biogenesis of peroxisomes occurs during migration of intestinal epithelial cells along the crypt-villus axis and that peroxisomal oxidases contribute substantially to the biochemical maturation of enterocytes.     

Fluorescence banding in four species of Microtidae: an analysis of the evolutive changes of the constitutive heterochromatin

Three different fluorochrome and specific counterstain combination (DAPI/AMD, DA/DAPI and CMA/DA) treatments were applied to the chromosomes of four Microtidae (Rodentia) species. The results complete the data obtained in our previous paper (Burgos, M., Jiménez, R., & Dìaz de la Guardia, R., Genome 30:540–546, 1988) and prove that the changes in the constitutive heterochromatin in the evolution of the karyotypes of these species are not only due to gain or loss of heterochromatin, but are qualitative with respect to their nucleotide composition, repeated base pair organization or DNA-protein complex modification. These variations lead to the differential response to the fluorescence dye combinations used.