Sedimentation polysaccharides

Physica.1 Sta.bihty, Physical stabiHty depends primarily on the purity of the enzyme. Impurities remaining from the fermentation broth may precipitate or form a hazy solution. Unwanted sedimentation is often related to Ca " or acidic polysaccharides. The solubiHty of some enzymes can be increased by optimizing the ionic strength or changing the dielectric constant of the solution by a dding low molecular-weight polyols. 

Polysaccharide Polydispersity and Simple Shape Analysis by Sedimentation Velocity... 

For a polydisperse solution—the hallmark of solutions of polysaccharides—s (and s ) will be a weight average [30,38,39]. If the solution contains more than one discrete (macromolecular) species—e.g. a mixture of different polysaccharides, the polydispersity will be manifested by asymmetry in the sedimenting boundary or, if the species have significantly different values for S2o,w. discrete boundaries are resolved (Fig. 2b [29]). 

Fig. 4 Sedimentation velocity g (s) profiles for starch polysaccharides using DCDT+. The profiles correspond to the radial displacement plots of Fig. 2. a Potato amylose, sample concentration 8 mg/ml in 90% in dimethyl sulphoxide. Rotor speed was 50 000 rpm at a temperature of 20 °C. b Wheat starch (containing amylose, left peak and the faster moving amylopectin, right peak), (total) sample concentration 8 mg/ml in 90% dimethyl sulphoxide. Rotor speed was 35 000 rpm at a temperature of 20 °C. From [29]...

A sedimentation coefficient distribution—either c s) versus 5 or g (s) vs. s—for a polysaccharide can also be converted into an apparent molecular weight distribution if the conformation of the polysaccharide is known or can... 

Polysaccharide Molecular Weight Analysis by Sedimentation Equilibrium... 

Molecular weights of polysaccharides in solution can also be measured by osmotic pressure and light scattering. Osmotic pressure yields the number average molecular weight, which can be usefully used with Mw from sedimentation equilibrium as a measure of polydispersity Preston and Wik [28] have done this for example with hyaluronic acid. The ratio Mw/Mn the polydispersity index is often given as a measure of polydispersity, and can be related to the width of a molecular weight distribution via the well-known Herdan [96] relation ... 

The sedimentation coefficient provides a useful indicator of polysaccharide conformation and flexibility in solution, particiflarly if the dependence of on Mw is known [62]. There are two levels of approach (i) a general level in which we are delineating between overall conformation types (coil, rod, sphere) (ii) a more detailed representation where we are trying to specify particle aspect ratios in the case of rigid structures or persistence lengths for linear, flexible structures. 

Once a general conformation type or preliminary classification has been established it is possible to use sedimentation data to obtain more detailed information about polysaccharide conformation. For example, the low value of ks/[v 0 25 found for the bacterial polysaccharide xylinan has been considered to be due to asymmetry [115]. If we then assume a rigid structure the approximate theory of Rowe [36,37] can be applied in terms of a prolate ellipsoid of revolution to estimate the aspect ratio p L/d for a rod, where L is the rod length and d is its diameter) 80. 

The reactants are then mixed in various proportions, and the sedimentation ratio (scompiex/smucin)—the ratio of the sedimentation coefficient of the complex to that of the pure mucin itself—is used as the measure for mucoad-hesion. The ultra-violet absorption optics on the XL-A or XL-1 ultracentrifuge have been used as the main optical detection system. Although the polysaccharide is generally invisible in the near UV ( 280 nm), at the concentrations normally employed the mucin—in uncomplexed and complexed form—is detectable. 

From sedimentation and diffusion measurements, Ogston has determined the molecular weight of the fructans from both leafy cocksfoot grass (Dacty-lis glomerata) and Italian rye grass (Lolium italicum) to be 5,500.261 Both polysaccharides were polymolecular, and the data indicated a singly-branched structure for each. 

The specific polysaccharide of the dominant O somatic antigen of Shigella dysenteriae has been shown to be electrophoretically and ultra-centrifugally homogeneous, and to possess a molecular weight of 26,000 from sedimentation and diffusion measurements.2601... 

Naturally occurring compounds in sediments (lipids, polysaccharides, lignins, etc.) have also been determined by this method. The compounds generated from non-polluted sediments are completely different and easily discriminated from anthropogenic contributions. 

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