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At least 505 records · Page 28Linked to original sources
PubMed2002

Long-term adaptation to prism-induced inversion of the retinal images.

For 1 week, healthy human participants ( n=7) were devoid of normal vision by exposure to prism lenses that optically rotated their perceived world around the line of sight by 180 degrees. Adaptation to such prisms involved sustained and vigorous practice of the ability to redirect the unadapted efferent motor command; because prior to all visually guided movements, the to-be-executed efferent command was based on incorrect (prismatically reversed) spatial information. The time course of this sort of adaptation was systematically explored in Cooper-Shepard mental rotation (MR) tests and in naturalistic motor-tasks for the purpose of investigating whether mental rotations of the direction of the intended movement share common aspects with the process of MR. A control group ( n=7) intermittently exposed to the distorted spatial organization of the central visual field was studied in parallel. The main results were as follows: (a) the MR reaction times (RTs) day 1 with prisms appeared to be very similar to the normal RTs (day 1, no-prisms) with the one exception that subjects now responded within a prism (rotated) frame of spatial reference rather than within the environmentally upright. The visuomotor performance became grossly irregular and dysmetric. (b) The majority of the visuomotor adaptation functions began to level off on the 3rd day. (c) The increases in natural motor proficiency were accompanied by a systematic and noticeable decrease in magnitude of the MR Y-intercept obtained from the linear regression line calculated between each subject's RT and the various stimulus angles. MR slopes were stable through days 1-7 for both the experimental and control group. An increased correlation between rotational stimulus angle and RT suggested that the MR function also became progressively more tightly coupled to the stimulus angles. (d) Postadaptation measures of performance indicated the occurrence of selective and minimal adaptation in the natural motor tasks only. It is suggested that these results reflect an improved attentional (strategic) ability to replace incorrect (error producing) control signals with correct (error reducing) control signals. As a result, perceptual-motor start-up processes directly related to spatial coding and to the planning, initiation and correction of the intended direction of motor-or-mental movement improved while the subprocess ("stage") concerned with transformations of such movements remained unchanged. Visuomotor adaptation to inverting prisms engages, and thereby stimulates, a cortical system also invoked in the preparatory process of MR.

Adaptation, Physiological↗
PubMed2000

Optomotor course control in flies with largely asymmetric visual input.

We have studied freely flying and walking flies as well as flies flying in a flight simulator in order to discover how functionally blinding one of the eyes affects the fly's ability to move straight. It is hard to tell just by observing the animals' movements whether they have been deprived of vision in one eye. Statistical analysis is need to show that there are differences in the locomotory paths of monocular and binocular flies: monocular flies tend to turn slightly towards the side of the seeing eye. It is possible that the superimposed translational and rotational optic flow fields, generated on the trajectory of monocular flies, sum to zero net flow. This overall flow over the retina of the open eye might lead to a state of optomotor equilibrium.

Animals↗
PubMed2006

Morphology of hepatitis C and hepatitis B virus particles as detected by immunogold electron microscopy.

We performed indirect immunogold electron microscopy (EM) for immunological identification and characterization of hepatitis C virus (HCV). To clarify the morphology of HCV, an indirect immunogold EM of two plasma samples from patients with high HCV RNA titers was carried out using antibodies specific for the putative HCV envelope protein (E) 1. Spherical virus particles 55-65 nm in diameter with delicate spike projections were detected in the 1.14-1.16 g/ml fractions after sucrose density gradient centrifugation. Polyclonal and monoclonal antibodies to the putative HCV E1 specifically recognized these particles. In addition, immunogold EM of the samples was also performed to uncover the morphology of HCV core particles. Spherical particles 33-40 nm in diameter (average, 37 nm) were detected in the 1.22- to 1.25-g/ml fractions by conventional EM after sucrose density gradient centrifugation. Immunogold EM using rabbit polyclonal antibody (RR8) specific for the putative HCV core protein and colloidal gold-labeled goat antirabbit IgG showed binding of the gold particles with RR8. Some of the HCV core particles showed icosahedric morphology. Optical rotation technique showed that the HCV core particles exhibit sixfold symmetry and that the length of the regular hexagon side is approximately 20 nm, suggesting that they have an icosahedric structure. Further, the detection limit of the indirect immunogold EM was evaluated in 11 plasma samples from chronic hepatitis B patients with different degrees of hepatitis B virus (HBV) DNA titers using antihepatitis B surface antigen antibody. The study showed that the detection limit of virus using this method is 10(7) virions/ml.

DNA, Viral↗
PubMed2006

Studies on the microbial transformation of androst-1,4-dien-3,17-dione with Acremonium strictum.

The strain of Acremonium strictum PTCC 5282 was applied to investigate the biotransformation of androst-1,4-dien-3,17-dione (I; ADD). Microbial products obtained were purified by preparative TLC and the pure metabolites were characterized on the basis of their spectroscopic features (13C NMR, 1H NMR, FTIR, MS) and physical constants (melting points and optical rotations). The 15 alpha-Hydroxyandrost-1,4-dien-3,17-dione (II), 17 beta-hydroxyandrost-1,4-dien-3-one (III), androst-4-en-3,17-dione (IV; AD), 15 alpha-hydroxyandrost-4-en-3,17-dione (V), 15 alpha,17 beta-dihydroxyandrost-1,4-dien-3-one (VI) and testosterone (VII) were produced during this fermentation. Formation of the 15 alpha,17 beta-dihydroxy derivative of ADD is reported for the first time during steroid biotransformation. The bioconversion reactions observed were 1,2-hydrogenation, 15 alpha-hydroxylation and 17-ketone reduction. From the time course profile of this biotransformation, ketone reduction and 1,2-hydrogenation were observed from the first day of fermentation while 15 alpha-hydroxylation occurred from the third day. Optimum concentration of the substrate, which gave the maximum bioconversion efficiency, was 0.5 mg ml(-1) in one batch. The highest yield of the microbial products recorded in this work was achieved within the pH range 6.5-7.3 and at the temperature of 27 degrees C.

Acremonium↗
PubMed1990

Specificity of acceptor binding to Leuconostoc mesenteroides B-512F dextransucrase: binding and acceptor-product structure of alpha-methyl-D-glucopyranoside analogs modified at C-2, C-3, and C-4 by inversion of the hydroxyl and by replacement of the hydroxyl with hydrogen.

The specificity of acceptor binding to the active site of dextransucrase was studied by using alpha-methyl-D-glucopyranoside analogs modified at C-2, C-3, and C-4 positions by (a) inversion of the hydroxyl group and (b) replacement of the hydroxyl group with hydrogen. 2-Deoxy-alpha-methyl-D-glucopyranoside was synthesized from 2-deoxyglucose; 3- and 4-deoxy-alpha-methyl-D-glucopyranosides were synthesized from alpha-methyl-D-glucopyranoside; and alpha-methyl-D-allopyranoside was synthesized from D-glucose. The analogs were incubated with [14C]sucrose and dextransucrase, and the products were separated by thin-layer chromatography and quantitated by liquid scintillation spectrometry. Structures of the acceptor products were determined by methylation analyses and optical rotation. The relative effectiveness of the acceptor analogs in decreasing order were 2-deoxy, 2-inverted, 3-deoxy, 3-inverted, 4-inverted, and 4-deoxy. The enzyme transfers D-glucopyranose to the C-6 hydroxyl of analogs modified at C-2 and C-3, to the C-4 hydroxyl of 4-inverted, and to the C-3 hydroxyl of 4-deoxy analogs of alpha-methyl-D-glucopyranoside. The data indicate that the hydroxyl group at C-2 is not as important for acceptor binding as the hydroxyl groups at C-3 and C-4. The hydroxyl group at C-4 is particularly important as it determines the binding orientation of the alpha-methyl-D-glucopyranoside ring.

Glucosyltransferases↗
PubMed1976

The influence of salt on the aggregation state of spectrin from bovine erythrocyte membranes.

Sedimentation velocity and gel filtration experiments have been performed with bovine spectrin over a wide range of neutral salt concentrations. Increasing salt concentrations tend to increase both the sedimentation coefficient of spectrin and the elution volume of the protein from 4% agarose columns. No conformation change can be detected by means of optical rotation measurements as the salt concentration is raised. The results are incompatible with the hypothesis that salt causes the aggregation of spectrin, but are consistent with the existence of marked charge effects operative at low salt concentrations. In support of the charge effect hypothesis, acidic groups have been detected on the agarose gels, and ion-exclusion behaviour on the column has been observed with other proteins of similar size.

Animals↗
PubMed1976

The nature of alkylurea and urea denaturation of alpha-chymotrypsinogen.

The optical rotatory dispersion of alpha-chymotrypsinogen in aqueous solution became less levorotatory upon the addition of ethyl-, propyl-, or butylurea; less negative values for the Moffitt-Yang parameter, alphao, were also obatined. This change in optical rotation of alpha-chymotrypsinogen induced by the alkylureas was similar in direction and magnitude to that observed for alcohols but was opposite to that caused by unsubstituted urea. It appears, therefore, that the alkylureas share with the alcohols an ability to rearrange alpha-chymotrypsinogen into a non-native yet regularly ordered conformation. The effectiveness of the alkylureas and alcohols as denaturants for this protein increased in the order ethyl less than propyl less than butyl derivatives. An identical rank-order was observed for the ability of the alkylureas and alcohols to diminish attractive forces between aliphatic groups, as measured by a model system based upon the extent of aggregation of glass beads coated with methyl groups. These findings indicate that the denaturing action of alkylureas for alpha-chymotrypsinogen is a function of the substituted aliphatic group and is predominantly hydrophobic in character. Non-hydrophobic interactions of unsubstituted urea with alpha-chymotrypsinogen appear to be critical for unfolding of the protein to a random-coil configuration.

1-Propanol↗
PubMed1977

Solvent denaturation of globular proteins: unfolding by the monoalkyl- and dialkyl-substituted formamides and ureas.

The effects of the monoalkyl and dialkyl-substituted formamide series of denaturants on the native conformation of sperm whale myoglobin, horse heart cytochrome c, and Glycera dibranciata (single chain) hemoglobin have been investigated by spectral measurements in the Soret region (409 and 422 nm) and optical rotation measurements (265nm). The effectiveness of these two classes of protein denaturants is similar to the other straight-chain compounds of the urea, amide, and alcohol classes, examined in previous investigations from our laboratory. Their denaturing effectiveness is found to increase with increasing chain length or hydrocarbon content of the substituent alkyl groups. Application of the Peller and Flory equation to the denaturation data of the formamides shows that both the polar and the nonpolar group contributions to the protein-denaturant interactions have to be taken into account in order to correctly predict the observed denaturation midpoints. Additivity of the hydrophobic, KHø, and the polar, Kp, group contributions to the binding constants, KB = nKHø + Kp, with n = 1 or 2 for the mono- of the di-alkyl substituted denaturants gave best account of the experimental data. The KHø values used were based on free energy transfer data of various alkyl groups or the Scheraga-Nemethy theory of hydrophobic bonding. The assumption of group contributions of the denaturant to KB were also applied to the denaturation data of the unsubstituted amides and some examples of the monoalkyl and symmetrically substituted dialkyl ureas, taken from the literature.

Cytochrome c Group↗
PubMed1981

The chromatographic purification of native types I, II, and III collagens.

In this paper, a chromatographic method for the purification of native types I, II, and III collagen is described. The method consists of two consecutive gel permeation chromatography steps, followed by anion-exchange chromatography. The two consecutive gel permeation chromatography steps take advantage of the fact that collagens like other asymmetric molecules, elute anomalously late from gel permeation columns, thus allowing one to separate collagens from less asymmetric proteins of comparable molecular weight, notably gelatin, procollagen and higher molecular weight oligomers of collagen. The anion-exchange chromatography separates types I, II, and III collagens from each other with baseline resolution. The collagen products obtained from these procedures are at least 99% pure by a variety of criteria, and in the native state by the traditional criteria of optical rotation, intrinsic viscosity, solubility properties and resistance to non-collagenase proteases. Rat skin type I collagen prepared by this chromatographic method exhibits a higher and sharper thermal transition temperature than an otherwise identical sample of rat skin type I collagen prepared by fractional salt precipitation. In addition, the latter collagen is more susceptible to digestion by trypsin at 37 degrees C. We conclude that salt precipitation of the collagen per se is responsible for a lowering of the Tm values. Our observations indicate that the chromatographic purification of collagen preserves the native structure at a few select sites where high salt concentrations induce irreversible local imperfections of the three-dimensional structure.

Animals↗
PubMed1994

Low molecular weight dermatan sulfate as an antithrombotic agent. Structure-activity relationship studies.

A structure-activity relationship of low molecular weight dermatan sulfate was undertaken to understand better this new non-heparin, glycosaminoglycan-based antithrombotic agent. A dermatan sulfate prepared from bovine intestinal mucosa [average molecular weight (MWavg) 25,000], and currently in clinical trials as an antithrombotic agent, was used in this study. Dermatan sulfate was partially depolymerized using hydrogen peroxide and copper(II) as catalyst to MWavg 5600 to obtain a low molecular weight dermatan sulfate. This low molecular weight dermatan sulfate was then fractionated by gel permeation chromatography to obtain four subfractions having MWavg 7800, 5500, 4200 and 1950. The dermatan sulfate, low molecular weight dermatan sulfate and its subfractions showed substantially different optical rotations. The 1H-NMR spectroscopic analysis of dermatan sulfate samples showed some differences including increased content of GalpNAc4S6S residues and improved resolution in ring resonances for low molecular weight dermatan sulfate fractions, primarily the result of reduced molecular weight and lowered heterogeneity. Saccharide compositional analysis relied on chondroitin ABC lyase treatment followed by capillary electrophoresis. Polyacrylamide gel-based oligosaccharide mapping was also performed by treating dermatan sulfate samples with chondroitin B, AC and ABC lysases. These analyses showed increased amounts of sulfation as the MWavg decreased. In vitro bioassay showed maximum anti-Xa activity in the 4.2 kDa fraction and maximum heparin cofactor II-mediated anti-IIa activity in the 5.5 kDa fraction. The in vivo antithrombotic activity of these fractions was measured using a modified Wessler stasis thrombosis model. The 4.2 kDa fraction showed greater antithrombotic activity than the other low molecular weight dermatan sulfate fractions, dermatan sulfate, and low molecular weight dermatan sulfate. This enhanced activity may result from several structural features of the 4.2 kDa fraction including: a high content of 4,6- and 2,4-disulfated disaccharide sequences; the requirement of specific chain length; a change in the ratio of iduronic to glucuronic acid; and the presence of chondroitin ABC lyase resistant material.

Animals↗
PubMed1990

Structure of the type 5 capsular polysaccharide of Staphylococcus aureus.

The Staphylococcus aureus type 5 capsular polysaccharide is composed of 2-acetamido-2-deoxy-L-fucose (1 part), 2-acetamido-2-deoxy-D-fucose (1 part), and 2-acetamido-2-deoxy-D-mannuronic acid (1 part). On the basis of methylation analysis, optical rotation, high-field one- and two-dimensional 1H- and 13C-n.m.r. experiments, and selective cleavage with 70% aqueous hydrogen fluoride, the polysaccharide was found to be a partially O-acetylated (50%) polymer of the repeating trisaccharide unit, [----4)-3-O-Ac-beta-D-ManpNAcA-(1----4)-a-L-FucpNAc-(1----3) -beta-D-FucpNAc-(1----]n.

Carbohydrate Sequence↗
PubMed1995

Travelling on the potential energy surfaces of carbohydrates: comparative application of an exhaustive systematic conformational search with an heuristic search.

The calculated ensembles found by a heuristic conformational search algorithm, CICADA, for three small carbohydrates, ethyl beta-lactoside, methyl alpha-D-galactoside, and methyl beta-D-galactoside, are evaluated in terms of their ability to reproduce time-averaged optical rotation and NMR data. A unique dynamic model for methyl beta-D-galactoside has been obtained by fitting experimental NOESY volumes to the theoretical ones elaborated from the CICADA ensemble internuclear distances with the model-free formalism. In the case of ethyl beta-lactoside, the CICADA ensemble is compared to that of an exhaustive systematic grid-search method. The CICADA algorithm proved to be a very efficient method to find most of the important minima on even very complex potential energy surfaces, and the spectral quality of the CICADA ensemble was found to be of equal quality, if not superior, to that of the exhaustive systematic grid-search method. The CICADA algorithm has several advantages over other conformational search algorithms: (1) It has polynomial dependence of dimensions on computer time in contrast to the grid search, which has exponential dependence, (2) the conformations found are free of artificial harmonic constraint potentials, (3) it passes all barriers amongst families of conformations on conformational hypersurface but spends almost all its time in the essential highly populated areas, (4) the inherent properties of the algorithm make rigorous minimization criteria superfluous and provide good convergence behavior, and (5) as an important spin-off, it provides low-energy interconversion pathways that can, amongst others, be used for estimating adiabatic rotational barriers.

Algorithms↗