The photoreaction center of Rhodospirillum rubrum mutant strain F24.1

Rhodospirillum rubrum strain F24.1 is a spontaneous revertant of nonphototrophic mutant F24 derived from wild-type strain S1. Strain F24 shows no detectable photochemical activity and contains, at most, traces of the photoreaction center polypeptides. Strain F24.1 has a phototrophic growth rate close to that of the wild-type strain (Picorel, R., del Valle-Tascón, S. and Ramírez, J.M. (1977) Arch. Biophys. Biochem. 181, 665–670) but shows little photochemical activity. Light-induced absorbance changes in the near-infrared, photoinduced EPR signals and ferricyanide-elicited absorbance changes indicate that strain F24.1 has a photoreaction center content of 7–8% as compared to strain S1. Polyacrylamide gel electrophoresis of isolated F24.1 chromatophores shows the photoreaction center polypeptides to be present in amounts compatible with this value. Photoreaction center was prepared from strain F24.1 and showed no detectable difference with that of strain S1. It is concluded that strain F24.1 photosynthesis is due entirely to its residual 7–8% of typical photoreaction center.     

Electrophysiology of phagocytic membranes. II. Membrane potential and induction of slow hyperpolarizations in activated macrophages.

The potential differences measured on the cell surface and after penetration into the cytoplasm of activated macrophages are described. Linear regressions are made of the measured potential differences as functions of the tip potential of each microelectrode. The surface potential of the macrophage is not significantly different from zero. Mouse macrophages have a transmembrane potential of--26 mV, whereas in guinea-pig cells this value is--18 mV. The input resistances of guinea-pig cells are higher than those of mouse macrophages. The cytoplasmic location of the electrode was characterized both by fluorescent dye injection and by electric criteria. Slow membrane hyperpolarizations are directly elicited by mechanical stimulation. Electric responses evoked by current pulses were further characterized. Our results lead to the extablishment of objective criteria to validate intracellular recordings from macrophage.     

New syntheses of deuterated protoporphyrin-IX derivatives for heme protein nmr studies

An efficient total synthesis of 1,5-di(trideuteromethyl)protoporphyrin-IX (3) dimethyl ester from monopyrrole precursors is described, the synthesis proceeding through crystalline tripyrrene and a,c-biladiene salt intermediates. The 2- and 4-vinyl groups in (3) are formed from the corresponding (2-chloroethyl) substituents by way of base-promoted dehydrochlorination. In protio solvents, this synthetic step is shown to exchange out preferentially deuterons in the 1-methyl group, and this observation is exploited in an efficient synthesis of the 1,3-di(trideuteromethyl)protoporphyrin-IX (22) dimethyl ester from 2,4-diacetyldeuteroporphyrin-IX (20) dimethyl ester (which is in turn accessible from commercially available protoporphyrin-IX (5)). Thus, basic exchange in deuterated solvent of (20) gives the deuterated analog, which after reduction and dehydration gives the 1,3-di(trideuteromethyl)protoporphyrin-IX analog (22), in which the vinyl H₂ and propionic CH₂·CO functions have also become deuterated.     

Photosensitization in cattle grazing on pastures of Brahciaria decumbens Stapf infested with Pithomyces chartarum (Berk. & Curt.) M.B. Ellis

Aspects of photosensitization in bovines grazing on pastures of Brachiaria decumbens Stapf infested with Pithomyces chartarum (Berk. & Curt.) M.B. Ellis infested all pastures 45(2):117-136, 1978. This paper reports experimental studies on photosensitization in bovines grazing on different pastures of Brachiaria decumbens Stapf in the "Cerrados" region (Planaltina, DF). Climatic conditions, zinc content and occurence of fungi on pastures were investigated. Pithomyces chartarum (Berk. & Curt.) M.B. Ellis infested all pastures examined. Photosensitization was observed in one animal maintained on a pasture of B. decumbens formed with seeds from Australia. Clinical and necropsy data were similar to those related in literature for sporidesmin-intoxicated animals. An isolate of P. chartarum and samples of bovine bile were assayed for sporidesmin presence.     

Characterizing the Interaction between Root-knot Nematodes and Soil-borne Fungi which are Pathogenic to Passion Fruit (Passiflora Edulis)

For decades there have been anecdotal claims of synergistic interactions between plant-parasitic nematodes and soil-borne fungi causing decline of productivity of passion fruit (Passiflora edulis) orchards. An empirical confirmation of these disease complexes would impact disease management and plant breeding for resistance. To test those claims, we subjected passion fruit plants to single or concomitant parasitism by Meloidogyne javanica or M. incognita and Fusarium nirenbergiae or Neocosmospora sp. under controlled conditions. Non-inoculated plants served as control for the assays. The severity of shoot symptoms and variables related to plant growth, the extent of fungal lesions, and nematode reproduction were assessed to characterize the interactions. The shoot symptoms and effect on plant growth induced by the pathogens varied, but no synergy between the pathogens was observed. Moreover, the volume of tissue lesioned by the fungi was not affected by co-parasitism of the nematodes. Conversely, plant resistance to the nematodes was not affected by co-parasitism of the fungi. The interactions M. incognita-F. nirenbergiae, M. incognita-Neocosmospora sp., M. javanica-F. nirenbergiae, and M. javanica-Neocosmospora sp. were not synergistic as previously claimed, but instead neutral.     

Characterization of Lipids and Proteins Associated to the Cell Wall of the Acapsular Mutant Cryptococcus neoformans Cap 67

Cryptococcus neoformans is an opportunistic human pathogen that causes life‐threatening meningitis. In this fungus, the cell wall is exceptionally not the outermost structure due to the presence of a surrounding polysaccharide capsule, which has been highly studied. Considering that there is little information about C. neoformans cell wall composition, we aimed at describing proteins and lipids extractable from this organelle, using as model the acapsular mutant C. neoformans cap 67. Purified cell wall preparations were extracted with either chloroform/methanol or hot sodium dodecyl sulfate. Total lipids fractionated in silica gel 60 were analyzed by electrospray ionization tandem mass spectrometry (ESI‐MS/MS), while trypsin digested proteins were analyzed by liquid chromatography coupled to tandem mass spectrometry (LC‐MS/MS). We detected 25 phospholipid species among phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and phosphatidic acid. Two glycolipid species were identified as monohexosyl ceramides. We identified 192 noncovalently linked proteins belonging to different metabolic processes. Most proteins were classified as secretory, mainly via nonclassical mechanisms, suggesting a role for extracellular vesicles (EV) in transwall transportation. In concert with that, orthologs from 86% of these proteins have previously been reported both in fungal cell wall and/or in EV. The possible role of the presently described structures in fungal–host relationship is discussed.     

Distribution dynamics of South American savanna birds in response to Quaternary climate change

Several lines of evidence suggest that savannas currently distributed disjointedly in the southern and northern portions of South America might have been connected and disconnected many times during the Quaternary climatic fluctuations. Here, we investigated how climate change since the Last Interglacial may have modified the distribution of bird species associated with South American savannas. We evaluated the connections between South America's savannas using 10 broadly distributed species and the impact of climate changes in community composition using 18 species endemic to Cerrado. We fit ecological niche models to each of the 28 bird species to compare the potential distribution patterns for the Last Interglacial (120 kyr BP), the Last Glacial Maximum (21 kyr BP) and the present. Our results corroborated hypotheses of past connections between northern and southern blocks of savannas through three hypothetical corridors that existed along the Andes, Atlantic Coast and through central Amazonia. In addition, our results also suggested the existence of a fourth plausible corridor located along the Madeira River, crossing Amazonia from the southwest to the northeast. Finally, our analysis showed significant changes in the community composition dynamics of endemic Cerrado species. Our results further reinforce the notion that climate change has major impacts on the distribution of savanna species.     

α-Glucosidase inhibition by flavonoids: an in vitro and in silico structure–activity relationship study

α-Glucosidase inhibitors are described as the most effective in reducing post-prandial hyperglycaemia (PPHG) from all available anti-diabetic drugs used in the management of type 2 diabetes mellitus. As flavonoids are promising modulators of this enzyme’s activity, a panel of 44 flavonoids, organised in five groups, was screened for their inhibitory activity of α-glucosidase, based on in vitro structure–activity relationship studies. Inhibitory kinetic analysis and molecular docking calculations were also applied for selected compounds. A flavonoid with two catechol groups in A- and B-rings, together with a 3-OH group at C-ring, was the most active, presenting an IC₅₀ much lower than the one found for the most widely prescribed α-glucosidase inhibitor, acarbose. The present work suggests that several of the studied flavonoids have the potential to be used as alternatives for the regulation of PPHG.     

Specific regulation of SOD isoforms by NaCl and osmotic stress in leaves of the C3 halophyte Suaeda salsa L

The halophyte Suaeda salsa L., exposed to different NaCl concentrations (100 and 400 mmol/L) and polyethylene glycol (isoosomotic to 100 mmol/L NaCl) containing nutrient solutions under normal or K+-deficient conditions for 7 days, was used to study effects of NaCl salinity and osmotic stress on chlorophyll content, chlorophyll fluorescence characteristics, malonedialdehyde (MDA) content, and superoxide dismutase (SOD) isoform activities. Photosynthetic capacity was not decreased by NaCl treatment, indicating that S. salsa possesses an effective antioxidative response system for avoiding oxidative damage. Seven SOD activity bands were detected in S. salsa leaf extracts, including an Mn-SOD and several isoforms of Fe-SOD and CuZn-SOD. It turned out that NaCl salinity and osmotic stress lead to a differential regulation of distinct SOD isoenzymes. This differential regulation is suggested to play a major role in stress tolerance of S. salsa.     

VGJ phi, a novel filamentous phage of Vibrio cholerae, integrates into the same chromosomal site as CTX phi

We describe a novel filamentous phage, designated VGJ phi, isolated from strain SG25-1 of Vibrio cholerae O139, which infects all O1 (classical and El Tor) and O139 strains tested. The sequence of the 7,542 nucleotides of the phage genome reveals that VGJ phi has a distinctive region of 775 nucleotides and a conserved region with an overall genomic organization similar to that of previously characterized filamentous phages, such as CTX phi of V. cholerae and Ff phages of Escherichia coli. The conserved region carries 10 open reading frames (ORFs) coding for products homologous to previously reported peptides of other filamentous phages, and the distinctive region carries one ORF whose product is not homologous to any known peptide. VGJ phi, like other filamentous phages, uses a type IV pilus to infect V. cholerae; in this case, the pilus is the mannose-sensitive hemagglutinin. VGJ phi-infected V. cholerae overexpresses the product of one ORF of the phage (ORF112), which is similar to single-stranded DNA binding proteins of other filamentous phages. Once inside a cell, VGJ phi is able to integrate its genome into the same chromosomal attB site as CTX phi, entering into a lysogenic state. Additionally, we found an attP structure in VGJ phi, which is also conserved in several lysogenic filamentous phages from different bacterial hosts. Finally, since different filamentous phages seem to integrate into the bacterial dif locus by a general mechanism, we propose a model in which repeated integration events with different phages might have contributed to the evolution of the CTX chromosomal region in V. cholerae El Tor.