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At least 343 records · Page 19Linked to original sources
PubMed1984

Dissimilar rates in molecular evolution.

In this work we present an evolutionary tree based on the differences in the physico-chemical properties involved in amino acid substitutions, instead of considering, for its construction, only the number of changes between species. Phylogenetic trees were constructed from the differences in bulkiness, refractivity index, hydrophobicity, polarity and optical rotation of 9 vertebrate calcitonins. A correlation of the form y = a xb was found between the number of changes (x) and the differences in any given physico-chemical property (y). This correlation implies that the evolutionary time can not be evaluated directly from the number of changes between species.

Amino Acid Sequence↗
PubMed1977

Association-dissociation and denaturation behaviour of an oligomeric seed protein alpha-globulin of Sesamum indicum L. in acid and alkaline solutions.

The association-dissociation and denaturation behaviour of the major protein fraction, alpha-globulin of sesame seed (Sesamum indicum L.), in acid and alkaline solutions in the ranges of pH 4.2-1.5 and pH 7-12 have been studied. The results of gel filtration, fluorescence and viscosity measurements indicate dissociation and denaturation of the protein up to pH approximately 3. The difference spectrum in this region arises from a combination of dissociation, denaturation and charge effect on the chromophore. In still stronger acid solution, reassociation of the dissociated fraction takes place by hydrophobic interaction. In alkaline solution dissociation takes place around pH 8, and above pH 10 dissociation and denaturation proceed simultaneously as has been evidenced by sedimentation, fluorescence, spectral change, optical rotation and viscosity measurements. The phenolic group (pKInt=10.6) in the protein is abnormal and denaturation in alkaline solution is irreversible. Above pH 11.5 further dissociation of the protein takes place. Characteristic pH values of transition from 10.6-10.8 indicate that the transition of the protein involves a single step in alkaline solution.

Acids↗
PubMed1993

Salmonella typhimurium neuraminidase acts with inversion of configuration.

When the time course of the hydrolysis of identical solutions of p-nitrophenyl N-acetyl-alpha-D-neuraminide by Salmonella typhimurium neuraminidase is monitored by u.v. and by its optical rotation, the rotation change is synchronous with, or even marginally in advance of, the absorbance change. In experiments under the same conditions with influenza-virus neuraminidase, known to react with retention of configuration [Chong, Pegg, Taylor and von Itzstein (1992) Eur. J. Biochem. 207, 335-343], the rotation change is much slower than the absorbance change. The inverting, presumably single-displacement, mode of action of the S. typhimurium enzyme follows from these observations, and the position (92.5% beta) of the slowly established mutarotational equilibrium of N-acetylneuraminic acid [Friebolin, Kunzelmann, Supp, Brossmer, Keilich and Ziegler (1981) Tetrahedron Lett. 22, 1383-1386].

Kinetics↗
PubMed2006

Hofmeister effects in supramolecular and biological systems.

Specific ion effects, representative of near-universal Hofmeister phenomena, are illustrated in three different systems. These are the formation of supramolecular assemblies from cyclodextrins, the optical rotation of L-serine, and the growth rate of two kinds of microorganisms (Staphylococcus aureus and Pseudomonas aeruginosa). The strong specific ion effects can be correlated with the anion polarizabilities and related physico-chemical parameters. The results show the relevance of dispersion (non-electrostatic) forces in these phenomena.

Anions↗
PubMed1992

High resolution 13C-n.m.r. spectroscopy of 'mixed linkage' xylans.

Three xylan fractions, obtained by stepwise precipitation with ethanol, were analysed by 75-MHz 13C-n.m.r. spectroscopy. Diad frequencies, determined from the C-2 resonances, show that the (1----3)-linkages are interspersed throughout the chain rather than grouped contiguously. This type of distribution is in agreement with a random coil conformation and with the constancy of the optical rotation in solvents of different ionic strength and chaotropic power. These diad frequencies were compared with the theoretical values calculated for a random distribution from the ratio of (1----4)-:(1----3)-linkages in the 1H-n.m.r. spectra, and from the methylation analysis for one of the fractions.

Carbohydrate Conformation↗
PubMed1999

Erythrocytes stored in CPD SAG-mannitol: evaluation of their deformability.

The erythrocytes deformability of three blood samples coming from healthy donors has been evaluated by Laser-assisted Optical Rotational Cell Analyzer (LORCA). Blood samples were stored in CPD SAG-mannitol. The study of progressive reduction in the Elongation Index (EI) during the preservation may be used as way of evaluation of erythrocyte vitality in stored blood samples.

Adenine↗
PubMed1975

Stereochemical course of the adenosine triphosphate phosphoribosyltransferase reaction in histidine biosynthesis.

The product of the first reaction in histidine biosynthesis is shown by optical rotation measurements on three derivatives to have inverted, beta stereochemistry at the newly formed bond. This is in contrast to alpha linkage expected on the basis of previously observed exchange, specificity, and covalent intermediate phenomena. The postulate double displacement mechanism for adenosine triphosphate phosphoribosyltransferase must be modified to account for the product stereochemistry.

Adenosine Triphosphate↗
PubMed1996

Structure and conformation of acetan polysaccharide.

Acetan is an anionic bacterial polysaccharide. The chemical repeat unit consists of a cellobiose unit solubilised by attachment of a charged pentasaccharide sidechain to one of the glucose residues. The repeat unit contains two sites of acetylation. 1H and 13C NMR studies, coupled with both basic-methylation and mild-methylation studies, have shown that acetylation occurs at C6 on the (1,2)D-Man and the (1,34)D-Glc residues. A variety of techniques including NMR, optical rotation, circular dichroism and DSC show evidence for a thermoreversible conformational order (helix)-disorder (coil) transition for acetan in aqueous solution. The studies suggest that acetylation of the backbone does not prevent helix formation.

Acetylation↗
PubMed1986

Direct 1H n.m.r. determination of the stereochemical course of hydrolyses catalysed by glucanase components of the cellulase complex.

The stereochemical courses of the hydrolyses catalysed by three glycosidases have been determined directly by 1H nmr. The anomeric configuration of the initially formed product was ascertained in each case by observation of the chemical shift and coupling constant of the anomeric proton at the new hemiacetal centre. Two of the enzymes investigated, an endo-glucanase and an exo-glucanase are components of the cellulase complex of Cellulomonas fimi. The third enzyme is the beta-glucosidase from almond emulsin. Two of these enzymes, the exo-glucanase and the almond beta-glucosidase catalysed hydrolysis with retention of anomeric configuration, in agreement with previous observations on the almond enzyme. The endo-glucanase catalysed hydrolysis with inversion of configuration, this result being confirmed by optical rotation measurements. This 1H nmr approach has several advantages over other techniques in that it is applicable to a wide variety of glycosidases and substrates and it is non-destructive, allowing recovery of the enzyme.

Cellobiose↗
PubMed1973

Structure determination of the glycolipid sulfate from the extreme halophile Halobacterium cutirubrum.

A sulfur-containing glycolipid, accounting for ca. 25% of the total polar lipids, has been isolated from the extreme halophile Halobacterium cutirubrum. The ammonium salt of the lipid was found to have the molecular formula C(61)H(117)O(21)S.NH(4), and on strong acid hydrolysis it yielded 2,3-di-O-phytanyl-sn-glycerol, glucose, mannose, galactose, and sulfate in equimolar proportions. Infrared and NMR spectra indicated the presence of a secondary sulfate group. Solvolysis of the lipid in 0.004 m HCl in tetrahydrofuran resulted in rapid release of inorganic sulfate and formation of galactosyl-mannosyl-glucosyl diphytanyl glycerol ether. With higher acid concentration (0.25 m methanolic HCl), stepwise hydrolysis of monosaccharide units occurred, giving mannosyl-glucosyl glycerol diphytanyl ether and monoglucosyl glycerol diphytanyl ether. The position of attachment of the sugars and of the sulfate group was determined by methylation of the free acid form of the glycolipid sulfate, followed by acid hydrolysis and gas-liquid chromatographic analysis of the partially methylated sugars as the alditol acetates. The configuration of the glycosidic linkages was established both by optical rotation measurements and by specific enzymatic hydrolysis. The results obtained established the structure as 2,3-di-O-phytanyl-1-O-[beta-d-galactopyranosyl-3'-sulfate-(1' -->6')-O-alpha-d-mannopyranosyl-(1' --> 2')-O-alpha-d-glucopyranosyl]-sn-glycerol.

Chromatography↗
PubMed1999

Reduced deformability of erythrocytes as feature of congenital dyserythropoietic anaemia type II (HEMPAS).

In this study we report results regarding erythrocytes deformability in congenital dyserythropoietic anemia type II (HEMPAS) by the use of LORCA (Laser-assisted Optical Rotational Cell Analyzer). The reduced erythrocytes deformability observed in seven case of CDA II is caused by changes in the structure of glycoproteins due to the incomplete glycosylation of erythrocytic and erythroblastic membrane. Erythrocytes deformability (EI) was shown to be inversely related with mean corpuscular volume (MCV) and mean haemoglobin concentration (MCH).

Adolescent↗
PubMed1992

On the solution properties of bacterial polysaccharides of the gellan family.

The influence of side chains and substituents on the polyelectrolyte behaviour of aqueous solutions of polysaccharides of the gellan family has been studied. The results of conductimetric and potentiometric titrations suggest that each of these polysaccharides adopts a double-helix conformation. Deacetylation destabilises the helix of rhamsan and gellan, and optical rotation data confirm these results. The side chain in rhamsan is more flexible and is remote from the carboxylate groups, and the behavior of this polysaccharide is similar to that of gellan. Gelation of deacetylated rhamsan occurs in the presence of calcium ions. The intrinsic viscosity as a function of ionic strength depends on the structure of the polysaccharide and on the presence of acetyl groups.

Carbohydrate Conformation↗
PubMed1971

The effects of certain glycols, substituted glycols and related organic solvents on the thermal stability of soluble collagen.

The effects of a number of related diols, substituted diols and glycerol on the thermal stability of acid-soluble calf skin collagen were investigated. Thermal transition temperatures were determined by optical rotation measurement. Short-chain diols with terminal hydroxyl groups, i.e. ethylene glycol and propane-1,3-diol, stabilized the protein at all accessible concentrations. Stabilization was also observed with glycerol and diethylene glycol. Higher homologues in the diol series produced various effects, as did hydroxyl-group positional isomerism. Monoalkyl substitution of diols progressively lowered the denaturation temperature of collagen. Results are discussed in relation to possible mechanisms of perturbant action.

Animals↗
PubMed2004

Polarimetric assay for the medium-throughput determination of alpha-amino acid racemase activity.

A polarimetric assay has been developed for the identification of alpha-amino acid racemase activity. The setup consists of a microcuvette polarimeter (40 microL volume) connected to a pipetting robot for microtiter plates, a pump, and data processing. It could be demonstrated for a glutamate racemase from Lactobacillus fermentii, expressed in Escherichia coli, serving as model enzyme, that its activity can be determined from the time-dependent change of the optical rotation using l-glutamate as substrate. Thus, the specific activity was determined to 111.4 mdeg/min which corresponds to 45.7 micromol/min per mg purified enzyme. Moreover, a protocol was developed that allows the measurement of racemase activity from 96-well microtiter plates using purified enzymes. Thus, the method described can be used to determine racemase activity in an automatic manner. It should be also applicable for the screening of enzyme libraries created by directed evolution.

Amino Acid Isomerases↗
PubMed2001

On the structure of kappa/iota-hybrid carrageenans.

The coil-to-helix transition and temperature dependence of the viscosity of commercial kappa/iota-hybrid carrageenans produced by the red algae Sarcothalia crispata, Mazaella laminarioides, and Chondrus crispus were studied using rheometry and optical rotation. The structure of these kappa/iota-hybrid carrageenans was determined by 1H and 13C NMR spectroscopy combined with monosaccharide composition analysis. The coil-to-helix transitions, measured by polarimetry and rheometry, of the kappa/iota-hybrid carrageenans are significantly different from those of pure kappa- and iota-carrageenan, and from hand-made mixtures thereof. This provides evidence that the kappa/iota-hybrid carrageenans are mixed chains, containing both kappa- and iota-repeating units.

Carbohydrate Conformation↗
PubMed1999

Chiral high-performance liquid chromatography of N-octyl bicycloheptene dicarboximide and confirmatory studies using liquid chromatography-tandem mass spectrometry and two-dimensional nuclear magnetic resonance spectroscopy.

N-Octyl bicycloheptene dicarboximide (MGK 264) has exo and endo diastereomers. Each structure has a chiral center at the nitrogen side chain. Enantioselective separation of MGK 264 was achieved by normal-phase high-performance liquid chromatography (HPLC) using cellulose-based Chiralcel OD column with diode-array and optical rotation detectors. Peaks were isolated with the purpose of identifying their stereochemical structures. Molecular mass of the HPLC peaks and their structural information was determined by liquid chromatography-electrospray tandem mass spectrometry (LC-ES-MS-MS). A two-dimensional nuclear magnetic resonance (NMR) spectroscopic technique was used to establish the structural features. Correlation of the data obtained from chiral separation and NMR facilitated in unambiguous assignment of the HPLC peaks.

Chromatography, High Pressure Liquid↗
PubMed1996

Homochirality as the signature of life: the SETH Cigar.

A characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. It is therefore suggested that a search for extra-terrestrial life can be approached as a Search for Extra-Terrestrial Homochirality (SETH). A novel miniaturized space polarimeter, called the SETH Cigar, is described which could he used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. It is believed that homochirality will be found in the subsurface layers on Mars as a relic of extinct life.

Astronomy↗
PubMed1989

Interpretation of the renaturation kinetics of gelatin solutions.

Renaturation kinetics of dilute gelatin solutions are studied by optical rotation and u.v. absorption. Comparing initial slopes of renaturation curves for concentrations below 10 mg.ml-1, the rate limiting process appears as the sum of a constant rate intramolecular nucleation and a bimolecular nucleation. To fit the whole renaturation curves, a kinetic model using Monte Carlo calculations was tested, consisting of random nucleation, rapid total propagation and slow reversion depending on the size of helical segment. Mismatch on the final renaturation extent indicates that propagation is more limited than proposed.

Gelatin↗