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PubMed1998

NMR study of virenose and dihydrohydroxystreptose isolated from Coxiella burnetii phase I lipopolysaccharide.

A lipopolysaccharide (LPS) isolated from Coxiella burnettii in virulent phase I contains in its O-polysaccharide chain two unusual sugars, virenose (6-deoxy-3-C-methylgulose) and dihydrohydroxystreptose [3-C-(hydroxymethyl)lyxose]. The sugars were isolated from LPS I, after acid hydrolysis and removal of lipid A, by a combination of HPLC and preparative paper chromatography. Their enantiomeric forms and ring conformations were established from optical rotation and NMR data. Two-dimensional COSY, HSQC, and HMBC as well as one- and two-dimensional NOEs were used to assign all proton and carbon signals in both monosaccharides. Virenose was found to be the D-gulo enantiomer with the 4C1 ring conformation and dihydrohydroxystreptose was shown to be the L-lyxo enantiomer also with the 4C1 conformation. The latter sugar was reported [S. Schramek, J. Radziejewska-Lebrecht, and H. Mayer, Eur. J. Biochem., 148 (1985) 455-461] to be present in LPS I in a furanose form, and it appears that a furanose to pyranose tautomerization took place in the course of the isolation procedure.

Carbohydrate Conformation↗
PubMed1976

Effects of the stereo-configuration of the hydroxyl group in 4-hydroxyproline on the triple-helical structures formed by homogenous peptides resembling collagen.

To explore further the recent demonstration that hydroxyproline stabilizes the triple-helical structure of collagen, two peptides containing allohydroxyproline, (aHyp-Pro-Gly)10 and (Pro-aHyp-Gly)10, were synthesized by a modified Merrifield technique which yields products of defined molecular weight. Examination of the peptides by optical rotation and circular dichroism showed that neither of them formed triple-helical structures in aqueous solution. Since the peptides had less tendency than (Pro-Hyp-Gly)10 to become helical, the results demonstrated that the trans-4-hydroxyl group of hydroxyproline makes a specific contribution to stability of the triple helix formed by (Pro-Hyp-Gly)10. Since the peptides also had less tendency than (Pro-Pro-Gly10 to become helical, the results further demonstrated that the cis-4-hydroxyl group on allohydroxyproline decreases the stability of the triple helix. The observations provided direct support for previous data indicating that incorporation of proline analogues such as allohydroxyproline into pro-alpha chains during procollagen biosynthesis prevents the polypeptides from becoming triple helical.

Binding Sites↗
PubMed2004

Chiral liquid chromatography contribution to the determination of the absolute configuration of enantiomers.

The review covers examples in which chiral HPLC, as a source of pure enantiomers, has been combined with classical methods (X-ray, vibrational circular dichroism (VCD), enzymatic resolutions, nuclear magnetic resonance (NMR) techniques, optical rotation, circular dichroism (CD)) for the on- or off-line determination of absolute configuration of enantiomers. Furthermore, it is outlined that chiral HPLC, which associates enantioseparation process and classical purification process, opens new perspectives in the classical determination of absolute configuration by chemical correlation or chemical interconversion methods. The review also contains a discussion about the various approaches to predict the absolute configuration from the retention behavior of the enantiomers on chiral stationary phases (CSPs). Some examples illustrate the advantages and limitations of molecular modeling methods and the use of chiral recognition models. The assumptions underlying some of these methods are critically analyzed and some possible emerging new strategies are outlined.

Chemical Phenomena↗
PubMedDate not supplied

Side-chain interactions and conformation in alpha-helical poly(gamma-phenacyl L-glutamate). Aggregation in dilute solutions.

The behavior of alpha-helical poly(gamma-phenacyl L-glutamate) (PPLG) has been studied by hydrodynamic, optical rotation, dielectric, and nmr measurements in different solvents. Special attention has been paid to side-chain interactions which depend on the ease of solvation of the phenacyl chromophore. Thus, in hexafluoro-2-propanol the circular dichroism spectrum is very similar to that usually observed for an alpha helix, and hydrogen bonding was shown to occur between the solvent and phenacyl CO group. In other heliocogenic solvents, side chain-side chain interactions occur. In dimethylformamide and pyridine they give rise at low temperature and low concentrations to an aggregation phenomenon whose molecular mechanism implies a molecular weight dependent folding of the molecules. Models for the side-chain conformation are proposed for the polymer in the solid state on the basis of infrared dichroism.

Binding Sites↗
PubMed1974

Chemical and physical properties of an arabinogalactan-peptide from wheat endosperm.

1. An arabinogalactan-peptide from wheat endosperm was studied by using physicochemical techniques and some aspects of its chemical structure were determined. 2. The arabinogalactan-peptide is a non-associating, polydisperse macromolecule ([unk]=22000) which exhibits only minor non-ideal effects in aqueous solution. 3. Examination of the products of partial acid hydrolysis of the polysaccharide component showed that arabinose is present in the alpha-l-arabinofuranosyl configuration, and i.r.-absorption spectroscopy and optical-rotation studies suggest that the d-galactopyranose residues are linked by glycosidic linkages in the beta-anomeric configuration. 4. The arabinogalactan is linked to a peptide which represents 8% (w/w) of the arabinogalactan-peptide and which may be present as a molecular core. Partial degradation of the polymer by successive treatment with oxalic acid and NaOH showed that the linkage between polysaccharide and peptide involves galactose and hydroxyproline residues and is glycosidic in nature. A tentative model is proposed for the structure of the wheat endosperm arabinogalactan-peptide. 5. The subcellular location and function of the arabinogalactan-peptide is discussed in relation to previous work with related molecules.

Amino Acids↗
PubMed1989

(-)-(S)-flunoxaprofen and (-)-(S)-naproxen isocyanate: two new fluorescent chiral derivatizing agents for an enantiospecific determination of primary and secondary amines.

The synthesis and analytical testing of two new fluorescent chiral derivatizing agents (-)-(S)-flunoxaprofen and (-)-(S)-naproxen isocyanate, is described. In a few simple steps the free carboxylic acids [(S)-flunoxaprofen and (S)-naproxen] are activated with ethyl chloroformate/sodium azide and transformed to the corresponding isocyanates. The crystalline reaction products display high enantiomeric and chemical purity and stability. The direction of the optical rotation of both substances is inverse to that of the corresponding carboxylic acids. At ambient temperature the reagents swiftly react with primary and secondary amines, yielding highly fluorescent ureas. The applicability of the two reagents for the resolution of racemic amines was tested with a number of pharmaceuticals (antiarrhythmics, beta-adrenergic antagonists, calcium channel blockers, centrally acting antidepressants). The diastereoisomeric derivatives were efficiently resolved and separated from side-products by means of normal and reversed-phase high-performance liquid chromatography (HPLC). The use and sufficient sensitivity of the two reagents for pharmacokinetic studies were demonstrated with a determination of plasma levels of propranolol enantiomers after oral administration of the racemic drug [80 mg (R,S)-propranolol-HCl] to two volunteers.

Amines↗
PubMed1983

Synthesis and antitumor activity of 7- and 9-(6'-deoxy-alpha-L-talofuranosyl) hypoxanthine and 9-(6'-deoxy-alpha-L-talofuranosyl)-6-thiopurine.

Reaction of 6-deoxy-2,3,5-tris-O-(p-nitrobenzoyl)-L-talofuranosyl bromide (1) with the trimethylsilyl derivative of hypoxanthine, followed by removal of blocking groups, afforded 9- (6) and 7-(6'-deoxy-alpha-L-talofuranosyl)hypoxanthine (7). A study of the published optical rotations and circular dichroic (CD) spectra of pentofuranosylpurines and of (6'-deoxy-beta-D-allo- and -alpha-L-talofuranosyl)purines prepared here suggests that the sign of rotation and the sign of the longer wavelength Cotton effect is determined solely by the configuration of C-1' and its position of attachment to the purine ring. For C-1' R nucleosides, the sign is negative for N-9-linked purine nucleosides and positive for the N-7-linked isomers, and vice versa for C-1'S purine nucleosides. Reaction of 1 with the trimethylsilyl derivative of 6-chloropurine afforded 4, which upon treatment with thiourea and deblocking yielded 9-(6'-deoxy-alpha-L-talofuranosyl)-6-thiopurine (8). Unlike the previously prepared 7-(6'-deoxy-beta-D-allofuranosyl) hypoxanthine which strongly inhibited purine nucleoside phosphorylase, compounds 6-8 did not inhibit this enzyme. Compound 8 significantly inhibited the growth of L1210 tumor cells in vitro and in vivo.

Animals↗
PubMed2002

Separation of oxazepam, lorazepam, and temazepam enantiomers by HPLC on a derivatized cyclodextrin-bonded phase: application to the determination of oxazepam in plasma.

The enantioselective high-performance liquid chromatography (HPLC) of three racemic 3-hydroxybenzodiazepines, oxazepam (Oxa), lorazepam (Lor), and temazepam (Tem), is a difficult operation because of the spontaneous chiral inversion in polar solvent. To solve this problem, we have developed an HPLC method based on a chiral Cyclobond I-2000 RSP column, maintained at 12 degrees C, and a reversed mobile phase (acetonitrile in 1% triethylamine acetate buffer, TEAA) at a flow rate of 0.4 ml/min. Peaks were detected by a photodiode-array detector at 230 nm for quantification and by an optical rotation detector for identification of (+) and (-) enantiomers. The results showed that peak resolutions of Oxa, Lor, and Tem enantiomers, analyzed under the same conditions, were 3.2, 2.0, and 1.8, respectively. For the determination of Oxa enantiomers in plasma of rabbits, extraction with diethyl ether at pH 1.5, a polar organic mobile phase, and a Cyclobond I-2000 SP column were used. Other analytical conditions were the same as previously described. Blood samples were immediately cooled at 4 degrees C and centrifuged at 0 degrees C for the collection of plasma. The results showed a difference in plasma S(+)- and R(-)-oxazepam concentrations in rabbits. No racemization of S(+)- or R(-)-Oxa enantiomers, added alone to blank plasma, was observed after extraction and enantioselective HPLC analysis.

Animals↗
PubMed1993

Polarimetry and 13C n.m.r. show that the hydrolyses of beta-D-glucopyranosyl fluoride by beta(1-->3)-glucanases from Phanerochaete chrysosporium and Sporotrichum dimorphosporum have opposite stereochemistries.

The time courses of optical rotation and fluoride ion release during hydrolysis of beta-D-glucopyranosyl fluoride by the beta(1-->3)-glucanase of Phanerochaete chrysosporium (J. L. Copa-Patiño and P. Broda, unpublished work) indicated that the initial sugar product was beta-D-glucopyranose. This was confirmed by monitoring the hydrolysis of 1-[13C]beta-D-glucopyranosyl fluoride by this enzyme with 13C n.m.r. (without proton decoupling). The same two techniques were used to confirm that hydrolysis of beta-D-glucopyranosyl fluoride by the exo beta(-->3)-glucanase of 'Basidiomycete QM 806' (identified as Sporotrichum dimorphosporum) yielded alpha-glucopyranose as first sugar product, in accordance with previous results using laminarin as substrate [Parrish and Reese (1963) Carbohydr. Res. 3, 424-429; Nelson (1970) J. Biol. Chem. 245, 869-872].

Basidiomycota↗
PubMed1992

Thermally induced chain exchange of frog alpha beta-tropomyosin.

The thermally induced unfolding of the alpha-helix of Rana esculenta alpha alpha, alpha beta and beta beta tropomyosin and two tryptic fragments approximately corresponding to the N- and C-terminal halves of alpha beta have been investigated by use of optical rotation, circular dichroism and UV difference spectroscopy. Reversible unfolding transitions of alpha alpha and beta beta occur around 49 degrees C and 32 degrees C, respectively. The helix unfolding of alpha beta shows two major transitions at 36 degrees C and 48 degrees C, with only the latter being reversible. The major unfolding transitions of each of the N- and C-terminal alpha beta peptides roughly correspond to the low and high temperature transitions of intact alpha beta, respectively. This suggests that the unfolding of alpha beta could be due to unfolding of two independent domains in alpha beta. UV difference data, crosslinking and chromatography results show, however, that the unfolding of alpha beta at 36 degrees C is due to chain exchange with the formation of alpha alpha homodimers and largely unfolded beta monomers, and that the transition at 48 degrees C is due to unfolding of alpha alpha dimers.

Animals↗
PubMed1982

Concentration dependence of the order-disorder transition of carrageenans. Further confirmatory evidence for the double helix in solution.

The temperature-induced changes in optical rotation which are associated with the order-disorder transition of carrageenans have been analysed to investigate the concentration dependence and hence to attempt to derive the number of polysaccharide chains involved in the ordered species at equilibrium. The consequences of the known polydispersity have been analysed by computer-modelling and it is shown that this need not cause misleading results. For iota-carrageenan segments of 0.1 M NaCl and 0.1 M KCl solution the results point to a two-chain state and therefore support the proposed double helix model. For chi-carrageenan segments the apparent average number of molecules involved in the ordered state at equilibrium is 3.7, suggesting that if double helices form here they aggregate further. The method of investigation may be generally applicable to measuring the number of chains which associate in ordered states in aqueous solutions of polysaccharides.

Carrageenan↗
PubMed2001

Red blood cell aggregation measurements in whole blood and in fibrinogen solutions by different methods.

Red blood cell (RBC) aggregation is an important component of whole blood viscosity, especially at low shear rates, and is the major cause of the non-Newtonian flow properties of normal blood. In different laboratories several methods are used to determine RBC aggregation, therefore the standardization of aggregation measurements is especially important for getting comparable results. Aggregation indices of 62 human blood samples were determined by two different methods; LORCA (Laser-assisted Optical Rotational Cell Analyzer) and Myrenne aggregometers and related to plasma fibrinogen concentration. Our results show closer correlation values between RBC aggregation and fibrinogen concentration, when RBC aggregation was measured by LORCA (p<0.001), although correlation could be revealed with Myrenne, when plasma fibrinogen level was less than 4.5 g/l. Correlation coefficient between aggregation indices measured by LORCA and Myrenne aggregometers was also closer below this fibrinogen level. In vitro examination of RBC aggregation in fibrinogen solutions showed that higher fibrinogen concentration results in higher RBC aggregation only up to a certain level similarly to that found in human whole blood samples. Our results show that plasma fibrinogen level has an important, concentration dependent effect on RBC aggregation in human blood, but above a certain level it may not cause further aggregate formation.

Adult↗
PubMedDate not supplied

[Acid-alkaline equilibrium of the ferri-leg-hemoglobin of the lupine (Lupinus luteus L.) Spectral studies].

Influence of pH was studied on the absorption spectra (340-670 nm) and on the curves of abnormal dispersion of optic rotation (220-270 nm) of the lupine ferri-leg-hemoglobin (Lb). pH range of the existence of the lupine Lb native form was determined (pH 5.5-11.0 at 20-25degrees C). It has been shown that not only met-hydroxy transition (which is in a complicated manner connected with the ionization of both ligand-bound water and certain amino acid residues of globin) but the ionization of a group with pK approximately 5, too, in the native molecule produces a heterotropic effect onto the haem. Complex analysis of the acidic and alkaline denaturation evidences that these processes are cooperative and proceed via several stages. pK values and the number of tyrosine residues were determined; it has been shown that these amino acid moieties are "buried" in the protein molecule. The results are discussed on the basis of a tentative model of the lupine Lb spatial suggested by the authors.

Amino Acids↗
PubMed2003

Thermoreversible gelation of kappa-carrageenan: relation between conformational transition and aggregation.

We have studied, by optical rotation dispersion, light scattering and rheology, the kappa-Carrageenan system to elucidate the processes involved in gel formation (on decreasing the temperature) and gel melting (on increasing the temperature). Our results show that, on decreasing the temperature, a conformational transition from coils to double helices first occurs, followed by aggregation of the double helices into domains and gel formation at appropriate polymer concentration. Structural details of this sequence are better revealed by re-heating the system. Melting appears as a two-step process characterized by first a conformational change of helices involved in junction zones between aggregates, followed by the conformational transition of the helices inside the aggregates. These helices can regain the coil conformation only when the aggregates melt at higher temperature, in full agreement with the old 'domain' model. The full description of the sol-gel mechanism of this system can be useful in the search for new methods to control the gel texture, a relevant property for many industrial applications.

Carrageenan↗
PubMed2004

Gelation of gellan gum aqueous solutions studied by polarization modulation spectroscopy.

Circular birefringence (CB, or optical rotation) and linear birefringence (LB) were measured for gellan gum aqueous solutions with and without salt to examine the gelling system in the helical structure as well as in the orientation. It was found that gelling samples with salt show nonzero LB values, whereas LB is zero for the samples without salt even in the gel state. This difference can be explained by the thermal deformation of the system containing anisotropic aggregations of helices formed with the shielding effect of the added salt on the intramolecular and intermolecular electrostatic repulsions. Considering that the presence of LB in the system affects the estimation of CB, we developed an original procedure of the CB measurement to eliminate the contribution of LB. It was shown that our methods for eliminating the contribution of LB can improve the CB measurement for the gellan gum gel. The temperature dependence of [alpha] for the samples with salt in the gel state is quite different from that for the samples without salt, suggesting that the aggregates of helices in the samples containing a high concentration of salt form a supramolecular structure that contributes to CB.

Carbohydrate Conformation↗
PubMed1974

Cathepsin B1. A lysosomal enzyme that degrades native collagen.

1. Experiments were made to determine whether the purified lysosomal proteinases, cathepsins B1 and D, degrade acid-soluble collagen in solution, reconstituted collagen fibrils, insoluble collagen or gelatin. 2. At acid pH values cathepsin B1 released (14)C-labelled peptides from collagen fibrils reconstituted at neutral pH from soluble collagen. The purified enzyme required activation by cysteine and EDTA and was inhibited by 4-chloromercuribenzoate, by the chloromethyl ketones derived from tosyl-lysine and acetyltetra-alanine and by human alpha(2)-macroglobulin. 3. Cathepsin B1 degraded collagen in solution, the pH optimum being pH4.5-5.0. The initial action was cleavage of the non-helical region containing the cross-link; this was seen as a decrease in viscosity with no change in optical rotation. The enzyme also attacked the helical region of collagen by a mechanism different from that of mammalian neutral collagenase. No discrete intermediate products of a specific size were observed in segment-long-spacing crystalloids (measured as native collagen molecules aligned with N-termini together along the long axis) or as separate peaks on gel filtration chromatography. This suggests that once an alpha-chain was attacked it was rapidly degraded to low-molecular-weight peptides. 4. Cathepsin B1 degraded insoluble collagen with a pH optimum below 4; this value is lower than that found for the soluble substrate, and a possible explanation is given. 5. The lysosomal carboxyl proteinase, cathepsin D, had no action on collagen or gelatin at pH3.0. Neither cathepsin B1 nor D cleaved Pz-Pro-Leu-Gly-Pro-d-Arg. 6. Cathepsin B1 activity was shown to be essential for the degradation of collagen by lysosomal extracts. 7. Cathepsin B1 may provide an alternative route for collagen breakdown in physiological and pathological situations.

Carbon Radioisotopes↗
PubMedDate not supplied

Chondroitin product selection for the glucosamine/chondroitin arthritis intervention trial.

OBJECTIVE: To select a high-quality chondroitin dosage form and/or an appropriate source of sodium chondroitin for the National Institutes of Health's Glucosamine/Chondroitin Arthritis Intervention Trial (GAIT). DESIGN: Controlled experimental trials. SETTING: Laboratory. PATIENTS OR PARTICIPANTS: Not applicable. INTERVENTIONS: Commercially available chondroitin products were reviewed, and purified sodium chondroitin from two suppliers was evaluated through tests (infrared and near-infrared identification, moisture content, pH, optical rotation, color and clarity of aqueous solutions prepared from the powders, protein contamination, total residue following ignition and nitrogen content, determination of sodium chondroitin molecular weight, disaccharide analysis, and measurement of chondroitin, sodium, and total glycosaminoglycan content) and an onsite supplier audit. MAIN OUTCOME MEASURES: Purity, potency, and quality of sodium chondroitin powders. RESULTS: No commercially available chondroitin product was deemed appropriate for use in GAIT. Samples of sodium chondroitin powder from two suppliers exhibited similar disaccharide and glycosaminoglycan content. Each contained approximately 2% hyaluronic acid and 8%-9% unsulfated disaccharide. Potency was inconsistent across groups, which might have resulted from different analytical methods and choice of reference standard. Mean potency obtained by five separate methods ranged from 82.2% to 95.5% for one supplier, 92.5% to 110.1% for another, and 95.1% to 112.5% for a commercially obtained reference standard. Critical issues raised by the results include choice of reference standard, selection of assay method, and the consistent appearance of an unidentifiable contaminant present in all three lots from one supplier. CONCLUSION: This blinded study determined methods to identify acceptable agents and provided results, which, in addition to regulatory compliance supplier audits, formed the basis for chondroitin product selection in GAIT.

Chondroitin↗
PubMed2006

Rheological properties of erythrocytes in patients suffering from erysipelas. Examination with LORCA device.

The rheological properties of erythrocytes: elongation and the aggregation, as well as basic peripheral blood parameters: RBC number, hematocrit, MCV, MCH, MCHC reticulocytes, fibrinogen level, ESR, and glucose level were studied in a group of erysipelas patients. The concentration of malonyl dialdehyde (MDA) in erythrocytes was also measured, as an indicator of oxidative stress exerted. The study involved 18 erysipelas patients and 18 healthy subjects. The rheological properties and the aggregation of erythrocytes were studied with the use of a LORCA instrument (Laser-assisted Optical Rotational Cell Analyser). Differences were found in elongation index (EI) between the blood control (C) and patients (P), with an increase of this value only at 0.58 Pa shear stress and at 1.13 Pa shear stress. Upstroke were used as the indexes of RBC deformability, and the following aggregation parameters: intensity of light scattering in the prior disaggregation (Isc dis) - C - 43.0 au (arbitrary units), P - 44.8 au, time when cells are round and not aggregated (Isc top) - C - 51.6 au, P - 49.3 au, the amplitude of aggregation, the difference between Isc max and Isc min (AMP) - C - 39.9 au, P - 28.7 au, aggregation index (AI) - C - 64.6%, P - 70.0%, time for reach one half of the maximum aggregation (t(1/2)) - C - 2.0 s, P - 1.5 s, threshold shear stress, the lowest force that breaks the aggregation formed (Y(thr)) in P exceed 170% control group were measured. A decrease in the elasticity of erythrocytes in erysipelas patients was associated with the simultaneous increase of MDA - C - 0.08 nM/mgHb, P - 0.11 nM/mgHb content in the membranes of red blood cells. Basic peripheral blood parameters studied in patients with erysipelas did not differ significantly from the control group except for WBC, fibrinogen (C - 3.8 g/l, P - 7.8 g/l), and ESR (C - 6.1 mm/h, P - 45.4 mm/h) which were significantly higher.

Aged↗