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At least 487 records · Page 27Linked to original sources
PubMed1993

Immobilisation of levansucrase on calcium phosphate gel strongly increases its polymerase activity.

The catalytic properties of levansucrase bound to hydroxyapatite were studied as a possible model for enzyme behaviour when associated in vivo to matrices such as the cell wall of bacteria or tooth surfaces. The activity of the immobilised enzyme was mainly directed towards its polymerase activity. The yield of levan reached 85%. The kcat of the enzyme for sucrose transformation was increased and the Km for this substrate was unmodified. These properties allow the design of a system for the large-scale production of high-molecular-weight branched-chain levan in vitro in high yield.

Bacillus subtilis↗
PubMed1993

Fructo-oligosaccharides from Urginea maritima.

Fructo-oligosaccharides from red squill (Urginea maritima) were isolated by precipitation with methanol, GPC on Biogel P2/P4, and reversed-phase HPLC. Structures of the tri- and tetra-saccharides were verified by the reductive cleavage method. A tetrasaccharide that contained both (2-->1)- and (2-->6)-linked beta-D-Fru f residues was isolated. The higher fractions from GPC were analysed by the reductive cleavage method without prior purification by reversed-phase HPLC. The mode of biosynthesis of sinistrin is discussed.

Carbohydrate Conformation↗
PubMed1995

Reductive cleavage of glycosides with borane complexes in the presence of boron trifluoride etherate.

Mixtures consisting of five equivalents each of borane.methyl sulfide and boron trifluoride etherate per equivalent of acetal or five equivalents of various amine-borane complexes and 10 equivalents of boron trifluoride etherate readily accomplished reductive cleavage of the glycosidic linkages of several per-O-methylated monosaccharides and polysaccharides. In all cases, the expected products were obtained in the expected molar proportions and no artifactual products were observed. Reductive-cleavage analysis using these reagents is particularly convenient because the reagents themselves are easy to handle and because subsequent acetylation of the products is accomplished in situ.

Acetylation↗
PubMed1988

Characterization of a T-cell clone recognizing idiotypes as tumor-associated antigens.

Although heterogeneous T cells recognizing idiotypic determinants have been demonstrated to occur spontaneously in vitro or to be expanded by immunization with antigen or idiotype, their in vitro propagation and cloning was not successful. These previous studies have relied extensively on soluble immunoglobulin to induce proliferation of idiotype-specific T cells. This report describes a unique approach to obtain a stable T-cell clone specific for a monoclonal beta 2-6 fructosan binding myeloma ABPC48 (BALB/c origin), bearing well-defined A48 regulatory idiotopes. Following repeated immunizations with ABPC48 myeloma protein of C.B/R3 mice (H-2d, VHb, CHa), which differ only in the VH locus from BALB/c mice (H-2d, VHa CHa), several stable T-cell clones were obtained after stimulation in vitro with ABPC48 myeloma cells. The proliferation of a T-cell clone A48.B2 was observed with irradiated myeloma cells or hybridomas producing antibodies bearing A48 idiotype encoded by genes deriving from the VH 441-4 family. Proliferation of the clone did not occur with soluble ABPC48 myeloma protein or with Sepharose 4B-bound ABPC48 myeloma protein. Both anti-A48Id and anti-Iad monoclonal antibodies can specifically inhibit the proliferation of this clone when stimulated with ABPC48 myeloma cells. These results demonstrate recognition of idiotypes on B-cell tumours by T cells and implicate the role of class II major histocompatibility complex determinants in this cellular interaction.

Animals↗
PubMed1990

Hemorrhage in mice produces alterations in intestinal B cell repertoires.

Abnormalities in immune response play a major role in the increased susceptibility to infection after hemorrhage and trauma. Infections occurring after injury often originate in the intestine. In order to determine the effects of hemorrhage on intestinal B cell function, we examined hemorrhage-induced alterations in available (clonal precursors) and actual (plasma cells) B cell repertoires among intestinal lamina propria and Peyer's patch cells. Hemorrhage resulted in complete suppression of the increase in levan-specific lamina propria and Peyer's patch plasma cell numbers following oral immunization with this bacterial polysaccharide antigen. The absolute frequency of clonal precursors specific for levan among lamina propria B cells decreased by more than twofold following hemorrhage. These results demonstrate that hemorrhage produces marked alterations in intestinal B cell repertoires, which may contribute to postinjury abnormalities in host defenses.

Animals↗
PubMed1986

Slow cytotoxicity of the polysaccharide levan on tumor cells in vitro.

Previous studies have shown that 1 h preincubation with levan caused a sharp decrease in tumorigenicity of tumor cells, although cell viability was not affected. In the present study, the possibility that levan might change the sensitivity of Lewis lung carcinoma cells to the host immune system and that levan might cause delayed damage were tested. Cell morphology, DNA synthesis, cell multiplication and viability as well as osmotic fragility were followed during several days in culture. Levan was found not to affect cell immunogenicity. The polysaccharide destroyed tumor cells by a rather peculiar mechanism: after a seemingly normal or even enhanced growth in culture during 3-5 days, cells suddenly burst. During the apparently normal growth, several morphological changes were observed: cell volume increased, cytoplasm swelled by apparent water uptake and some cells contained two or more nuclei. Levan-treated cells were found to be more susceptible to osmotic shock than non-treated cells. The reason for the sudden cell death could be a gradual increase in volume, up to a point which is no more compatible with membrane integrity, resulting in cell lysis.

Animals↗
PubMed1975

Dependence of the cardiac uptake of digitalis glycosides on the extracellular calcium concentration in guinea pig isolated hearts.

The purpose of the present study was to investigate, at the myocardial level, the divergent influences of Ca2+ on the action of various cardiotonic steroids. Therefore, the cardiac uptake of 3-H-digitoxin and 3-H-digitoxin was studied in experiments on guinea pig isolated hearts. The following results were obtained: with digitoxin the increase of the extracellular calcium concentration from 0.45 upto 7.2 mM resulted in a concomitant decrease of the myocardial glycoside uptake from about 1.8 nmoles/g wet weight down to about 1.2 nmoles/g wet weight. Similar results were obtained when digoxin uptake was studied under the same conditions: with 0.45 mM Ca2+ about 0.6 nmoles/g wet weight were bound, increasing the calcium concentration upto 7.2 mM lead to a concomitant decrease of the cardiac digoxin uptake down to about 0.45 nmoles/g wet weight. Despite the different physicochemical behaviour of these two drugs and the different amounts of drug present in the hearts the influence of Ca2+ was almost identical if calculated on a relative basis. So far, no experimental based explanation can be given for the above discrepancies. Other possible interpretations are discussed.

Animals↗
PubMed1995

Effect of fermentable fructo-oligosaccharides on mineral, nitrogen and energy digestive balance in the rat.

In the present study, we have assessed the apparent retention of gross energy, nitrogen and Ca, Mg, Fe, Zn and Cu in rats receiving a diet supplemented with fermentable fructo-oligosaccharides with high and low degree of polymerization. Feeding 10% Raftilose (degree of polymerization: 4.8) or 10% Raftiline (degree of polymerization: 10) decreased to the same extent (a) the fecal excretion of all the minerals, despite an increase in total fecal mass excretion leading to an improvement of the absorption of Ca, Mg, Fe and Zn; (b) total gross energy absorption; and (c) led to an increase in the faecal excretion and to a decreased urinary excretion of nitrogen, suggesting a displacement of part of nitrogen excretion towards the large intestine. Feeding fermentable fructo-oligosaccharides may thus constitute a good way to counteract syndromes resulting from hyperammonemia or disturbed Fe, Ca, Mg and Zn homeostasis.

Animals↗
PubMed1985

The expression of a private idiotope requires pretreatment with noncomplementary anti-idiotypic antibodies.

The levan-binding ABPC48 myeloma protein is characterized by 3 idiotopes, (Ids), defined by 3 syngeneic monoclonal anti-idiotypic antibodies (IDA 10, IDA 16 and IDA 17). When BALB/c mice are immunized with levan, they produce anti-levan antibodies, some of which carry the Id 10 and Id 16 but not the Id 17 determinants. In the present study, we attempted to induce the synthesis of Id 17 positive anti-levan molecules. We found that immunization with IDA 17 antibodies alone was ineffective in inducing an Id 17 positive anti-levan response. By contrast, successive immunizations with IDA 10, IDA 16 and IDA 17 antibodies resulted in the synthesis of Id 17 positive anti-levan immunoglobulins. The synthesis of these molecules was concommitant with the induction of Id 10 and Id 16 positive anti-levan antibodies. Thus our data suggest that the Id 17 determinant on anti-levan antibodies is coexpressed with Id 10 and Id 16, and that successive anti-idiotypic treatment may result in the selective expansion of rare ABPC48 cross-reactive idiotype B-cell clone precursors.

Animals↗
PubMed1985

Immune response induced by a single or several syngeneic monoclonal antiABPC48 antiidiotypic antibodies: no predominant coexpression of ABPC48 idiotopes.

BALB/c mice were immunized with monoclonal BALB/c antibodies IDA10, IDA16 and IDA17 raised against the BALB/c ABPC48 myeloma protein. Several procedures of immunization--copolymers with lipopolysaccharide or keyhole limpet hemocyanin, simultaneous or sequential injections of different IDAs--were performed in an attempt to orient the immune response towards the production of ABPC48-like idiotypes. We used a binding assay which identifies two idiotopes on the same molecule to measure the population of antibodies induced in these responses. The expression of ABPC48 cross-reactive idiotypes in immune sera was analyzed. The results show that, with all immunization protocols, immune responses to different monoclonal antiidiotypic antibodies are mostly independent of each other: the coexpression of ABPC48 idiotopes, either private or recurrent on the induced antibodies, is rarely found; it makes it difficult to discriminate by a serological approach between cross-reactive idiotypes and anti-antiidiotypic antibodies. We discuss the interest of combining molecular and serological approaches to identify these two populations of antibodies.

Animals↗
PubMed1992

Readthrough of the Bacillus subtilis stop codon produces an extended enzyme displaying a higher polymerase activity.

It has been generally accepted that the structural sacB gene of Bacillus subtilis levansucrase encodes a 50,000 Da extracellular protein. However, examination of the DNA sequence of the sacB flanking regions shows a putative open reading frame coding for a 20 amino acid peptide downstream immediately following the terminal TAA stop codon. By site-directed mutagenesis we have changed this stop codon to a glutamine codon. This stop codon readthrough leads to the synthesis and secretion by B. subtilis of a levansucrase possessing an extended polypeptide chain. The extended levansucrase has a molecular weight of 53,000 with a new carboxyl-terminus, rich in basic and hydrophobic amino acids and possessing one cysteine residue. This enzyme synthesizes fructosyl polymer levan of higher molecular weight than the shorter levansucrase. The increase in molecular weight was achieved by increasing the number of branches. These results suggest that the C-terminal part of the enzyme plays a specific role in the degree of branching of the synthesized polymer. Moreover, the extended enzyme is able to form an active dimer from two polypeptide chains linked by an S-S bridge.

Amino Acid Sequence↗
PubMed1983

Effect of administration schedule on the levan-cyclophosphamide combined treatment of Lewis lung carcinoma.

Combined treatment with levan and cyclophosphamide (CY) was applied intratumorally to Lewis lung carcinoma tumors in C57B1 mice on day 5 after tumor cell inoculation. Although on that day levan alone had no effect and CY alone caused only temporary regression of tumors, the combined CY-levan treatment caused 60% cure. Levan given before CY was almost as effective as simultaneous administration of both drugs on day 5. Delaying the administration of levan after CY treatment reduced the therapeutic effect. It is concluded that timing in relation to tumor cell inoculation as well as the order of administration of drugs, determine the degree of therapeutic efficacy. In tumor chemo-immunotherapy the final effect is probably due not only to the anti-tumoral effect per se of each drug, but also to the fact that the two agents have an effect on the immune system. Since the immune response may change during tumor development, the effect of timing of administration of an immunomodulator and certainly to two immunomodulators, can be crucial.

Animals↗