Human and bovine group B streptococci (types II and III) variations in the virulence for pregnant mice

Virulence of 10 human and 10 bovine isolates (5 type II and 5 type III of each origin) of group B streptococci (GBS) was measured in two experimental mouse models. In the first model, mice were intraperitoneally (i.p.) infected, and the 50% lethal doses (LD₅₀) were significantly lower for human isolates than for bovine isolates. In the second model, abortion and lethality were recorded for mice infected intravenously (i.v.) on day 13 of pregnancy. All 10 human isolates induced abortions, whereas only 5 bovine isolates did so. There was no relationship between 50% abortive doses determined for 9 isolates (4 human and 5 bovine) and the LD₅₀ values. Post-partum lethality was significantly correlated with LD₅₀ values.Our studies suggested that the lethality test for nonpregnant mice and the abortion test for pregnant mice were not redundant and that the latter would be a useful additional model for identification of virulence factors of GBS.     

O-glycosylation of dipeptides using β-galactosidase activity of Achatina achatina digestive juice

Summary Enzymatic O-glycosylation of dipeptide derivatives containing a serine residue in the N or C terminal position and alanine or glycine as the second amino acid was achieved using the transgalactosylation activity of -galactosidase from the Achatina achatina digestive juice. Reactions were performed with lactose as glycosyl donor and the dipeptide ethyl (or methyl) esters N-protected by a benzyloxycarbonyl group (Z) as glycosyl acceptors. Yields of galactosyl-dipeptide derivatives were much higher than those obtained with the E.coli -galactosidase as catalyst.     

Allelic polymorphism in the hamster oviductin gene is due to a variable number of mucin-like tandem repeats

Oviductins are high-molecular-weight glycoproteins specifically secreted by the oviduct. These proteins bind to the zona pellucida of the ovulated oocyte and remain associated with the embryo during its transit in the oviduct. They may be involved in fertilization and early embryonic development. In order to explore their putative biological function, the cDNA sequence corresponding to oviductin in the golden hamster was determined. We found that the deduced amino acid sequence of this heavily O-glycosylated protein presents characteristics typical of mucins, including serine- or threonine-rich tandem repeats. Analysis of several cDNA clones and of genomic DNA revealed the presence of a single copy gene with two frequent alleles differing in the number of repeats. Comparison with oviductin sequences from other mammals indicates a high degree of conservation amongst species, except for the repeat region which shows divergence, notably in the number of repeats. Based on its biochemical and genetic properties, hamster oviductin can now be classified as a secretory mucin. This concept provides a new insight in the elucidation of its biological role: oviductin could possibly provide the oviduct and the oocyte with a protective coating ensuring normal tubal function and embryonic development. © 1995 wiley-Liss, Inc.     

Sequence of the novel joints present in the amplified DNA of N-phosphonacetyl-L-aspartate resistant Drosophila cells: Implication on the mechanisms of amplification in these cells

Summary— We have previously shown the presence, in the amplified DNA of a Drosophila cell line resistant to N-phosphonacetyl-L-aspartate (PALA), of two units of 150 kb and 120 kb respectively duplicated and amplified. The two joints (J1 and J2) linking these units as well as their respective wild-type counterparts have been sequenced. Sequence analysis indicates that a region of the Drosophila genome which corresponds to the proximal boundary of the 150 kb unit is common to both joints. In addition to this common region, the J1 junction possesses a 26-nucleotide sequence belonging to the J2 junction. This indicates that the J2 junction was the first formed, and that J1, therefore, results from recombination between J2 and a region of the wild-type genome 120 kb distal to J2. Sequence analysis also reveals that the joints result from illegitimate recombination between unrelated regions. AT-rich sequences, strand bias composition and putative topoisomerase I and II sites were found in at least one of the two parental sequences involved in the formation of the joints. On the basis of these results we can hypothesize that after two illegitimate recombinations between sister chromatids, leading first to J2 and then to J1, the amplification may have arisen by a series of homologous (unequal crossing-over) or illegitimate recombinations, or by an intrachromosomal rolling circle.     

Determination of non-protein-bound iron in human synovial fluid by high-performance liquid chromatography with electrochemical detection

Non-protein-bound iron in human synovial fluid was determined using high-performance liquid chromatography with electrochemical detection. The procedure was based on the separation of the iron—diethylenetriaminepentaacetic acid (DPTA) complex formed directly on a chromatographic column containing an anion-exchange resin followed by electrochemical detection. The method enabled more than 0.1 μM Fe(III) to be determined with an injection volume of 10 μl. A mixture of synovial fluid, 20 μM DTPA and acetate buffer was incubated in the presence and absence of superoxide (O⁻₂) generated by a xanthine—xanthine oxidase system and was ultrafiltered through a 30 000 molecular mass cut-off filter. No iron was detected in the ultrafiltrate at physiological pH. However, the presence of iron was observed in the ultrafiltrate at low pH, and O⁻₂ and decreased pH, iron may be released into the synovial fluid.     

Charge Transfer Modulated Activity of Carbon‐Based Electrocatalysts

Electrocatalysis is the most important electrode reactions for many energy storage and conversion devices, which are considered a key part of the resolution of the energy crisis. Toward this end, design of efficient electrocatalysts is of critical significance. While extensive research has been extended to develop excellent electrocatalysts, the fundamental understanding of the relationship between the electronic and structural properties of electrocatalysts and the catalytic activity must remain a priority. In this review, the activity modulation of electrocatalysts by charge transfer effects, including intramolecular and intermolecular charge transfer, is systematically introduced. With suitable charge transfer modification, such as heteroatom doping, defect engineering, molecule functionalization, and heterojunctions, the electrocatalytic activity of carbon‐based electrocatalysts can be significantly boosted. The manipulation of the electronic structure of carbon‐based materials by charge transfer may serve as a fundamental mechanism for performance enhancement. After establishing an understanding of the relationship between catalytic activity and charge transfer, the opportunities and challenges for the design of electrocatalyst with charge transfer effects are discussed.