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At least 721 records · Page 40Linked to original sources
PubMed1979

Rapid helix--coil transitions in the S-2 region of myosin.

Temperature-jump studies on the long S-2 fragment (100,000 daltons) isolated from myosin show that this structure can undergo alpha-helix--random coil transitions in a time range approximating the cycle time of a crossbridge. Two relaxation times are observed after temperature jumps of 5 degrees C over the range 35--55 degrees C, one in the submillisecond (tau f) and the other in the millisecond (tau s) time ranges. Both processes exhibit maxima near the midpoint of the helix--coil transition (tm = 45 +/- 2 degrees C) as determined by optical rotation melt experiments. Similar results were observed for the low temperature transition (tm = 45 degrees C) of the myosin rod. Viscosity studies reveal that the S-2 particles has significant flexibility at physiological temperature. Results are considered in terms of the Huxley--Simmons and helix--coil transition models for force generation in muscle.

Animals↗
PubMed2003

Immunologically active O6-branched (1-->3)-beta-glucan from the lichen Thamnolia vermicularis var. subuliformis.

A lentinan-type gel-forming beta-glucan, Ths-2, has been isolated in about 1.5% yield from the alkali extract of the lichen Thamnolia vermicularis var. subuliformis, using ethanol fractionation, dialysis and gel filtration. The mean Mr of Ths-2 was determined by GP-HPLC to be 67 kD, and the optical rotation was measured to be -14 degrees. The structure of Ths-2 was further elucidated by methylation analysis by GC-MS, 1H- and 13C-NMR spectroscopy and selective enzymatic hydrolysis with exo-(1 --> 3)-beta-D-glucanase followed by analysis of oligosaccharides by HPAEC-PAD. Ths-2 was found to be consisting of a (1 --> 3)-beta-D-glucopyranosyl main chain with branches of a (1 --> 6) linked glucopyranosyl unit on every third unit of the main chain. Similar polysaccharide structures have been described from fungi, but this is the first report of a lentinan-type (1 --> 3)-beta-D-glucan from a lichen species. The immunomodulating activity of Ths-2 was tested in an in vitro anti-complementary assay, and proved to be strongly active.

Animals↗
PubMed1998

Red blood cell rigidification during cyclosporin therapy: a possible early warning signal for adverse reactions.

In a previous retrospective study with kidney-transplant patients, immunosuppressive treatment with Cyclosporin A (CsA) was found to be associated with impaired red blood cell (RBC) deformability. The aim of the present study was to evaluate and substantiate a possible causal relationship between the use of CsA and its effect on RBC deformability in a prospective study on non-transplant patients. Blood samples of 12 patients with psoriasis were taken before and after 2, 4, 8, 12 and 16 weeks of treatment with CsA (3-5 mg/day). Red cell deformability, expressed as Elongation Index (EI), was measured with the Laser-assisted Optical Rotational Cell Analyzer (LORCA), a new ektacytometric instrument. Mean values +/- SD for EI found after 16 weeks of treatment with cyclosporin (0.570 +/- 0.008) were significantly (p < 0.001) lower than the value before treatment (0.589 +/- 0.011). A dose-response relation could not be established within the small range of CsA doses used in this study. Irrespective of the dose, however, a significant correlation (r = -0.55; p = 0.0001) between duration of treatment and decrease in EI was demonstrated. In vitro incubation of blood with cyclosporin was not able to reproduce this effect, suggesting that a direct effect of the drug on RBCs is unlikely. Despite its use in relatively low doses, CsA causes a reduction in RBC deformability, an effect that increases during the course of treatment. It is suggested that this slow, but continuously increasing, RBC rigidification plays a role in the early pathogenesis of the adverse nephrotoxic complications frequently associated with this immunosuppressive regimen.

Cyclosporine↗
PubMedDate not supplied

A comparison of the physicochemical and immunological properties of the plant gum exudates of Acacia senegal (gum arabic) and Acacia seyal (gum tahla).

The physiochemical and immunological properties of three Sudanese gum arabic samples and four gum tahla samples (two Sudanese, one West African and one Tanzanian--Acacia seyal var. seyal) were compared. The optical rotation (ca -30 degrees) and rhamnose (12-14%), arabinose (24-29%), galactose (36-42%), glucuronic acid (16-17%), nitrogen (0.327-0.365%) and protein (2.16-2.41%) contents of the gum arabic samples were consistent with the FAO (1990) specification for Acacia gum. In contrast the gum tahla samples had positive [alpha]D values (+45 degrees to +54 degrees), lower rhamnose (3-4%) and higher arabinose (41-45%) contents and lower nitrogen (0.147-0.175%), and hence protein (0.97-1.15%), contents. All of the gum arabic samples precipitated with beta-glucosyl Yariv reagent and hence were shown to contain arabinogalactan-protein(s) (AGPs), whereas in all but one of the gum tahla samples AGPs were not detected. The strong interaction of gum tahla with a monoclonal antibody known to recognize arabinose residues present in AGPs and arabinogalactans (AGs) was consistent with the observed higher levels of arabinose present in the gum tahla samples relative to the gum arabic samples. The data presented confirm that there are a number of physicochemical and structural differences between gum arabic (A. senegal gum) and gum tahla (A. seyal gum), and that a quick and simple immunological technique (immunodot blots) using an antiAGP/AG monoclonal antibody (MAC 207) could be used to screen for the presence of gum tahla in gum arabic consignments.

Acacia↗
PubMedDate not supplied

Synthesis of 6-O-methyl ether of Scorzocreticin and Scorzocreticoside I, metabolites from Sorzonera cretica.

6-O-methyl ether of racemic scorzocreticin (1a) and its 8-O-beta-D-glucoside, scorzocreticoside I (1b), isolated from Greek endemic species Scorzonera cretica have been synthesized. 6,8-Dimethoxy-3-(4-methoxyphenyl)isocoumarin (3) was obtained by reaction of 3,5-dimethoxyhomophthalic acid (2) with 4-methoxy-benzoyl chloride at elevated temperature. Hydrolysis of isocoumarin (3) to keto acid (4) followed reduction and spontaneous cyclodehydration to afford ( +/- )-6,8-dimethoxy-3-(4-methoxyphenyl)-3,4-dihydroisocoumarin (5) which was regioselectively demethylated to ( +/- )-6-O-methylscorzocreticin (6). Glycosylation of the latter using 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide in the presence of silver carbonate in quinoline under Koenigs-Knorr conditions afforded 6-methoxy-8-O-glucoside tetraacetate (7) as a 1:1 diastereomeric mixture. Finally, deacetylation of (7) using sodium methoxide afforded the diastereomeric mixture of R and S 6-O-methylscorzocreticin 8-O-glucosides (8). The 6-O-methyl ether of natural scorzocreticoside I (1b) was separated and identified on the basis of sign of optical rotation.

Asteraceae↗
PubMed2005

Ring-expanded analogues of natural oxetanocin: (+) and (-) hydroxymethyl isodideoxyadenosine.

New enantiomeric isonucleoside analogues related to natural oxetanocin have been synthesized from D-glucosamine and D-glucose. The structures of the target compounds were confirmed by NMR, HRMS, UV, single crystal X-ray, and optical rotation data. Stability studies with respect to purine nucleoside phosphorylase and adenosine deaminase show that these compounds are not substrates. Antiviral results are discussed.

Adenine↗
PubMed1957

The solubility and properties of a purified ichthyocol in salt solutions of neutral pH.

1. Purified citrate-extracted ichthyocol obtained from carp swim bladders has been further characterized with respect to its content of certain amino acids and carbohydrate substances. 2. The degree of solubilization or dispersion of ichthyocol by solutions of certain salts maintained in the range of neutral pH and at a temperature of 0-2 degrees C. has been determined. 3. While a number of salts of monovalent cations had no significant solubilizing effects on ichthyocol, ammonium chloride in a concentration of 1 M did cause solution of the protein. 4. Sodium thiosulfate in a range of concentrations caused the solubilization of ichthyocol but was most effective in an intermediate concentration of 0.25 M. 5. Several salts of divalent cations, in particular the chlorides of calcium, magnesium, and barium, and magnesium thiosulfate in concentrations ranging from 0.3 to 1 M caused the immediate and complete solubilization of the ichthyocol. 6. Solutions of ichthyocol in calcium chloride, magnesium chloride, and sodium thiosulfate buffered or adjusted to pH 7.0, were studied with respect to intrinsic viscosity of the protein, optical rotation, ultracentrifugal sedimentation, and reconstitution into fibers. It was found in each case that the original characteristics of the collagen, as determined previously in acid solution, were maintained when the protein was dissolved in salt solutions of neutral pH. No evidence of denaturation or gelatinization could be found when ichthyocol was solubilized under the stated conditions. 7. Collagen in neutral solution with sodium thiosulfate, calcium chloride, or magnesium chloride was not attacked by trypsin as determined viscometrically at 20.0 degrees C., but was rapidly degraded by a purified bacterial collagenase.

Acids↗
PubMed1983

Monoclonal antibodies against chicken type V collagen: production, specificity, and use for immunocytochemical localization in embryonic cornea and other organs.

Two monoclonal antibodies have been produced against chick type V collagen and shown to be highly specific for separate, conformational dependent determinants within this molecule. When used for immunocytochemical tissue localization, these antibodies show that a major site for the in situ deposition of type V is within the extracellular matrices of many dense connective tissues. In these, however, it is largely in a form unavailable to the antibodies, thus requiring a specific "unmasking" treatment to obtain successful immunocytochemical staining. The specificity of these two IgG antibodies was determined by inhibition ELISA, in which only type V and no other known collagen shows inhibition. In ELISA, mixtures of the two antibodies give an additive binding reaction to the collagen, suggesting that each is against a different antigenic determinant. That both antigenic determinants are conformational dependent, being either in, or closely associated with, the collagen helix is demonstrated by the loss of antibody binding to molecules that have been thermally denatured. The temperature at which this occurs, as assayed by inhibition ELISA, is very similar to that at which the collagen helix melts, as determined by optical rotation. This gives strong additional evidence that the antibodies are directed against the collagen. The antibodies were used for indirect immunofluorescence analyses of cryostat sections of corneas and other organs from 17 to 18-day-old chick embryos. Of all tissues examined only Bowman's membrane gave a strong staining reaction with cryostat sections of unfixed material. Staining in other areas of the cornea and in other tissues was very light or nonexistent. When, however, sections were pretreated with pepsin dissolved in dilute HAc or, surprisingly, with the dilute HAc itself dramatic new staining by the antibodies was observed in most tissues examined. The staining, which was specific for the anti-type V collagen antibodies, was largely confined to extracellular matrices of dense connective tissues. Experiments using protease inhibitors suggested that the "unmasking" did not involve proteolysis. We do not yet know the mechanism of this unmasking; however, one possibility is that the dilute acid causes swelling or conformational changes in a type-V collagen-containing supramolecular structure. Further studies should allow us to determine whether this is the case.

Animals↗
PubMed1976

Immunochemical studies on blood groups LXII. Fractionation of hog and human A, H, and AH blood group active substance on insoluble immunoadsorbents of Dolichos and Lotus lectins.

The purified lectins from Lotus tetragonolobus and Dolichos biflorus were coupled to Sepharose 2B to make insoluble adsorbents for purification and fractionation of blood group A and H active glycoproteins. With both adsorbents, hog gastric mucin A + H blood substance (HGM), purified by phenol-ethanol precipitation, yielded fractions showing only A, only H, or AH activities. The AH fraction was obtained when the adsorbent column was overloaded with HGM and its A and H specificities seem to be carried on the same molecules since they were not separable by chromatography on either column. However A and H specificities of blood group substance from the stomach of a presumably heterozygous individual hog were both on the same molecules as they too could not be fractionated on either column. Analytical properties of the isolated fractions were generally similar to those of the unfractionated material, the purfied A substances had a higher galactosamine/fucose ratio than did the H substances. Although the original A + H showed very little specific optical rotation, the separated A and H substances rotated positively and negatively, respectively. The lectin-Sepharose adsorbents have also proven useful in isolating A or H substances directly from the crude commercial hog gastric mucin. Blood group A2 substance from a human ovarian cyst yielded two fractions on the Lotus-Sepharose column; the effluent did not interact with the Lotus lectin but precipitated the Ulex and Dolichos lectins and anti-A, and appears to contain type 1 H determinants. The other fraction reacted with Lotus and Ulex lectin as well as with Dolichos and anti-A.

ABO Blood-Group System↗
PubMed2000

Noninvasive glucose monitoring with optical heterodyne technique.

A novel optical polarimeter to sense the glucose level in vivo and noninvasively has been developed in the Institute of Radiological Science, National Yang Ming University. A 30-minute delay between the aqueous glucose and the blood glucose was observed in rabbit's eyeball. Currently, aqueous glucose in low concentration is being tested and discussed.

Animals↗
PubMed2006

Search for extraterrestrial life using chiral molecules: mandelate racemase as a test case.

We have investigated an enzymatic racemization reaction as a marker for extraterrestrial life, which resulted in a change in optical rotation of a mandelic acid over time, as measured by polarimetry. Mandelate racemase was active in aqueous buffer in a temperature range between 0 degrees C and 70 degrees C and also in concentrated ammonium salt solutions and water-in-oil microemulsions in a temperature range between -30 degrees C and 60-70 degrees C; however, the enzyme was not active in several organic cryosolvents. Thus, we have demonstrated that concentrated ammonium salt solutions and water-in-oil microemulsions, both of which are able to form on extraterrestrial planets and moons in the presence of liquid water, are suitable media for enzyme reactions at subzero temperatures. Kinetic data for the mandelate racemase reaction obtained by polarimetry, while reproducible and internally consistent, differed significantly from several sets of data obtained previously by other methods such as chromatography and hydrogen-deuterium exchange. However, we conclude that reactions yielding a polarimetric signal, such as the racemizations employed in this work, are suitable mechanisms by which to utilize a change in chirality over time as a tool to detect signs of life.

Buffers↗
PubMed2003

First synthesis of L-enantio-uracil dinucleotide.

L-Enantio-uracil dinucleotide, which consists of two L-uridylic acids and one pyrophosphate, was synthesized for the first time in our laboratory. Benzolyated L-uridine was prepared by a steroselective glycosylation of silylated uracil with L-1-acetoxy-2,3,5-tri-O-benzoylribose (L-ABR). After deprotection, L-uridine was converted to L-UP4U by the treatment of L-UMP morpholidate with triethyammonium pyrophosphate (TEA-PPi). Spectral data of synthesized L-UP4U are given in a reference. All spectral data were identical with those of the D-enantiomer except the optical rotation. It showed a positive value compared to the D-enantiomer having a negative value.

Nucleic Acid Conformation↗
PubMed1992

Reaction mechanism of glutamate racemase, a pyridoxal phosphate-independent amino acid racemase.

Glutamate racemase of Pediococcus pentosaceus contained no cofactor, and was completely inactivated by a thiol reagent. The role of a cysteine residue in the enzyme reaction was studied by chemical modification. The modification of this cysteine residue resulted in a concomitant loss of activity. DL-Glutamate protected the enzyme from inactivation. The inactivated enzyme was reactivated by addition of dithiothreitol. The racemization in 2H2O showed an overshoot in the optical rotation of glutamate before the substrate was completely racemized. This indicates that the removal of alpha-hydrogen is the rate determining step. During the racemization of D- or L-glutamate in 3H2O, tritium was incorporated preferentially into the product. Glutamate is racemized by the enzyme probably through a two base mechanism.

Amino Acid Isomerases↗
PubMed1982

A sulfated polysaccharide produced by an Arthrobacter species.

A new sulfated polysaccharide was isolated from the culture supernatant of a strain of Arthrobacter sp. The polysaccharide purified with quaternary ammonium salts consists of D-galactose, D-glucose, sulfate, phosphorus, glucosamine, muramic acid, alanine, glutamic acid, glycine, and LL-diaminopimelic acid in a molar ratio of 56 : 9.0 : 68 : 6.4 : 2.0 : 1.1 : 2.1 : 1.0 : 1.2 : 1.2. The presence of the two amino sugars and four amino acids suggests that the polysaccharide, which is principally a galactan sulfate, contains small amounts of so-called peptidoglycan and that it is derived from the bacterial cell-wall polysaccharide. Gel filtration indicates the heterogeneity of the purified polysaccharide in its peptidoglycan content and molecular size. The molecular weight of its major portion was estimated to be 2.3 X 10(4) by gel filtration. The fractions GS-I and GS-II, and GS-4M and GS-5M, which were obtained by fractionation of the polysaccharide on Sephacryl S-200 and Dowex 1-X2 (Cl- form), respectively, gave almost the same chemical composition as the original polysaccharide, except in the peptidoglycan content, indicating that this polysaccharide is a series of complexes composed of essentially equal, sulfated polysaccharide chains and peptidoglycan fragments in their various ratios. The polysaccharide has [alpha]D -36 degrees and is composed predominantly of beta-glycosidic linkages, as judged from its specific optical rotation (-37 degrees) and the infrared absorption (885 cm-1) of its desulfated material. It exhibits a potent antithrombin activity (ID50, 0.82 micrograms/ml). A possible partial structure of the polysaccharide is also discussed, based on the results of periodate oxidation, Smith degradation, and alkali treatment.

Arthrobacter↗
PubMed1983

Some properties of synthetic fucopyranosylserines and -threonines.

alpha Fuc-Ser, alpha Fuc-Thr, beta Fuc-Ser, and beta Fuc-Thr were synthesized stereoselectively in good yields, and their properties were investigated. beta-Fucosylserine (and -threonine) was synthesized by Koenigs-Knorr reaction of per-O-acetylfucopyranosyl bromide with N-carbobenzoxy-L-serine (and -threonine) benzyl ester using mercuric cyanide, followed by hydrogenolysis and deacetylation. alpha-Fucosylserine (and -threonine) was synthesized by the halide-ion catalyzed reaction of per-O-benzylfucopyranosyl bromide with the serine (and threonine) derivative described above, followed by hydrogenolysis. These substances each gave a single peak on an amino acid analyzer. The anomeric configurations of these compounds were determined by 1H-NMR spectroscopy, optical rotation measurement and enzymatic degradations of these compounds. On acid hydrolysis, alpha Fuc-Ser and alpha Fuc-Thr were more rapidly hydrolyzed than the corresponding beta-series compounds. Under mild alkaline conditions in the presence of sodium borohydride, per-protected beta Fuc-Thr released about 50% of fucose but free beta Fuc-Thr did not However, free alpha Fuc-Thr and beta Fuc-Thr were cleaved to give acetylated fucose during acetylation with acetic anhydride-pyridine. alpha-L-Fucosidases, which were purified from abalone and rabbit livers by affinity chromatography, acted very well on alpha Fuc-Ser and alpha Fuc-Thr, but not on the beta-series compounds.

Fucose↗
PubMed1986

Direct measurement of salicylphenolic glucuronide in human urine.

Indirect measurement of salicylphenolic glucuronide (SPG) has suggested that the formation of this metabolite from therapeutic doses of salicyclic acid (SA) is capacity-limited in humans. A direct high performance liquid chromatographic (HPLC) assay for SPG in human urine is described. SPG was prepared by a published method and purified by HPLC. On treatment with beta-glucuronidase, SPG yielded the expected amount of SA. Spectroscopic data, melting point, and optical rotation of the glucuronide and/or its triacetyl dimethyl ester derivative were consistent with the proposed structure. SPG was assayed using a 5-micron C18 column (temperature 55 degrees C) and fluorescence detection. A nonlinear gradient mobile phase at a flow rate of 2 ml/min was used, beginning with 100% 0.1 M pH 2.1 phosphate buffer and finishing with 84% buffer, 16% acetonitrile. Total run time was 25 min. Urine (10 microliter) was injected directly on the column, and quantitation was performed using urine standards. Within-run precision for SPG ranged from 1.2% at 150 mg/L to 2.4% at 5 mg/L. The limit of detection was less than 1 mg/L. A pilot study in two volunteers, each receiving a single 500-mg dose of sodium salicylate, was carried out to validate the usefulness of the assay.

Adult↗