Nominal Molecular Weight Cutoff Research Articles

Size fractionation of metals in wine using ultrafiltration

Ultrafiltration has been used to examine the size fractionation of lead, copper, iron, aluminium, calcium, potassium and sodium in white and red wines. Fractionation patterns demonstrated that the behaviour of lead is significantly diferent to the other metals considered. In red wine, there was a sudden decrease for lead between 100 000 and 30 000 nominal molecular weight cut off (NMWCO) and in white wine, a gradual decrease in the lead concentration was observed from 100 000 NMWCO. Iron was the only other metal which showed, for red wine, a size distribution pattern with a reduction in the iron concentration between 30 and 50% from 100 000 to 1000 NMWCO. Potential binding agents for lead and iron are discussed. The absence of any fractionation pattern for the other metals examined has been interpreted in terms of the metals existing as aquated cations (potassium and sodium), metal tartrate complexes (aluminium, copper and calcium) and either tartrate or phosphate for iron in white wine. The possibility of ultrafiltration disturbing kinetically facile processes, particularly for copper and calcium, is identified.

Protein Structure Change on Adherence to Ultrafiltration Membranes: An Examination by Electron Paramagnetic Resonance Spectroscopy

Electron paramagnetic resonance spectroscopy was used to examine changes in the distance between two spin-labels on hen egg lysozyme (HEL, 45 Å × 30 Å × 30 Å, 14,600 Da) when interacting with membranes during ultrafiltration (UF). Membranes with nominal molecular weight cutoff (MWCO) values ranging from 10,000 to 300,000 Da were used. Both cellulosic (hydrophilic) and polysulfone (hydrophobic) membranes were studied. The technique used is based on spin–spin interaction of protein-bound spin-labels that cause dipolar broadening of the EPR spectra. This line broadening is related to spin-label distance and was subsequently used to infer protein conformational changes. The results demonstrate that the distance between the two labels on HEL, while in aqueous solution, was approximately 14.4 Å. Using the known crystal structure of hen egg lysozyme, molecular computer modeling of the doubly labeled protein suggests that the most probable spin–spin distance in solution is 13.9 Å. This distance is in excellent agreement with our experimentally observed result. Protein–membrane interaction reduced this distance approximately by 5 Å, irrespective of the membrane morphology. It is speculated that the lack of variation seen in all the membranes, under our test conditions, may be due to limitations associated with spin-label locations.

Atomic Force Microscope Studies of Membranes: Surface Pore Structures of Diaflo Ultrafiltration Membranes

Noncontact atomic force microscopy (AFM) has been used to investigate the surface pore structure of eight Diaflo ultrafiltration membranes covering a range of nominal molecular weight cutoff (MWCO) from 3000 to 300,000 and manufactured from three different polymer types. Excellent high resolution images were obtained. Analysis of the pore images gave quantitative information on the surface pore structure, in particular the pore size distribution and surface roughness. Such data is compared to that obtained by other techniques. Noncontact AFM is a facile and informative means of studying the surface structure of porous materials such as synthetic membranes.

A comparison of monoclonal antibody productivity in different hollow fiber bioreactors

Cell culture in hollow fiber bioreactors has been used as a method for large-scale production of monoclonal antibodies, viruses, cell-associated proteins and cancer antigens. We have examined an important variable in culturing cells in hollow fiber bioreactors: bioreactor composition. Eight different bioreactor designs which varied in nominal molecular weight cutoff, surface area, fiber material and ultra filtration rate were compared in large-scale hollow fiber cultures. A standard protocol utilizing the hybridoma 3C11 (ATCC HB 8511) or African green monkey kidney cells (Vero cells, ATCC CRL 1587) was designed so that the only variable examined was the hollow fiber bioreactor in use. The results suggest that surface area has little effect on antibody productivity, while fiber composition and ultrafiltration rate may play an important role. Vero cell growth was affected by both fiber composition and ultrafiltration rate.

Poly(ethylene oxide)‐grafted thermoplastic membranes for use as cellular hybrid bio‐artificial organs in the central nervous system

Poly(acrylonitrile-co-vinyl chloride) (PAN/VC) anisotropic membranes were chemically modified with poly(ethylene oxide) (PEO) (5000 and 20,000 g/mol) by one of two aqueous reactions: (a) acid hydrolysis of the nitrile group to a carboxylic acid with which amine-terminated PEO (PEO-NH(2)) reacted or (b) base reduction of the nitrile group to an amine with which PEO-succinimide (PEO-SC) reacted. Approximately 1.3% of the bulk material was modified with PEO-NH(2) whereas 1.8 to 3.5% was modified with PEO-SC as determined by proton nuclear magnetic resonance ((1)H NMR) and attenuated total reflectance Fourier transform infrared (ATR FTIR) spectra. Approximately 50 to 75% less bovine serum albumin (BSA) adsorbed to PEO-grafted single skin fibers than to unmodified PAN/VC. Transport properties of modified and unmodified fibers were compared by passive diffusion, convective nominal molecular weight cutoff, and hydraulic permeability. Neither hydraulic permeability nor nominal molecular weight cutoff of BSA changed appreciably after surface modification with PEO indicating that pore structure was not adversely affected by the chemistry involved in grafting poly(ethylene oxide). However, in the absence of any membrane conditioning, the apparent diffusion of alpha-chymotrypsinogen (24,000 g/mol) was enhanced in PEO-grafted PAN/VC fibers possibly as a result of reduced sorption of the permeating protein. In vivo biocompatibility in the brain tissue of rats was judged by histological assessment of the host's cellular response to fibers implanted for 30 days; biocompatibility of both PAN/VC and PAN/VC-g-PEO was satisfactory but improved slightly with PEO grafting. (c) 1994 John Wiley & Sons, Inc.

Protein adsorption in polysulfone hollow fiber bioreactors used for serum‐free mammalian cell culture

The recovery of serum-free medium proteins from poly-sulfone hollow fiber bioreactors (HFBRs) was investigated. More than 99% of the initial transferrin was adsorbed to the hydrophobic hollow fibers within 2 h of HFBR operation. A methodology to minimize transferrin adsorption by pre-adsorption of bovine serum albumin (BSA) was developed. BSA adsorption on suspended cut fibers was virtually complete within 1 h. BSA-coated fibers adsorbed only 5% of the transferrin within 10 days, whereas uncoated cut fibers adsorbed more than 99% of the transferrin within 1 h. An improved HFBR startup procedure, using a BSA-coating step before inoculation, resulted in substantially higher transferrin recovery. Additional factors influenced extracapillary space (ECS) transferrin concentrations. Pronounced downstream polarization of transferrin was observed in the ECS. In addition, the 30-kDa nominal molecular weight cutoff ultrafiltration membranes rapidly leaked transferrin from the ECS to the lumen.

The surface structure and morphology of polyacrylonitrile membranes by atomic force microscopy

Contact and non-contact atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the surface structure and morphology of a 30,000 Da nominal molecular weight cut-off (NMWCO) polyacrylonitrile (PAN) membrane, and the results are compared. AFM microscopy indicates that this PAN ultrafiltration membrane has pores with diameters in the 12–20 nm size range and that these pores undergo little or no diminution in their sizes upon drying. In contrast, it was difficult to discern the pore structures by SEM. Both SEM and AFM revealed the presence of defects in the membrane which are believed to be surface extensions of the underlying macrovoid structures. However, a discrepancy exists in the sizes of these defects estimated by SEM and AFM. It is proposed that SEM reveals only the defects themselves but that the AFM yields images profiling the defects themselves and the surrounding depressions in the membrane surface formed by the rapid intrusion of water into the still-fluid substrate of the nascent membrane in which coagulation eventually occurs to produce the macrovoid structures.

Addition of sulphuric acid to high organic carbon lake water: Effects on macro-chemistry, aluminium, and iron

A humic lake of pH 5.6 was acidified with H2SO4 to pH 4.1. Measurements of total and hollow-fiber ultrafiltered samples were made after three different times of storage, before and after the acid treatment. The nominal molecular weight cutoff of the hollow-fiber membrane was 10 kDalton. Assuming a linear molecular weight distribution of the organic complexes present in solution, the average organic molecule had an average molecular weight of 12.8−08 kDalton (n=6). Not only Ca2+ and Mg2+, but also detectable amounts of Na+ and K+ was found to be present on high molecular weight forms. No significant change in the molecular weight distribution of these elements were observed after the pH decrease. Changes in the molecular weight distribution after the acid treatment were only observed for Fe and Al. Significant amounts of SO4 2− were present on high molecular weight forms. A small, but significant increase in the relative amounts of SO4 2− present on high molecular weight forms was observed after the pH lowering. Kinetic constraints were demonstrated for dissolution of Al and Fe. To some extent, kinetic constraints in the equilibrium distribution of cation/anion exchange reactions of Al, Fe, and SO4 2− were also observed. After the acid treatment, the cation exchange capacity (CEC) of the organic pool present was estimated to be at least 18.2±1.4 (n=3) μeq of positive charges per mg C, probably because the negative sites on the organic pool are either not totally protonated or occupied by other cations at pH 4.09. This CEC is of the same order as industrially made cation exchange resins.

Association of radionuclides with different molecular size fractions in soil solution: Implications for plant uptake

The feasibility of using hollow fibre ultrafiltration to determine the molecular size distribution of radionuclides in soil solution was investigated. As the soil solution is the intermediary phase in the soil-to-plant transfer of radionuclides, its physical and chemical composition plays a vital role in determining radionuclide uptake by plant roots. Soil solution samples were extracted from loam, peat and sand soils that had been artificially contaminated with 137Cs, 90Sr, 239Pu and 241Am six years previously as part of a five-year lysimeter study on radionuclide uptake to crops. Ultrafiltration of soil solution was performed using hollow fibre cartridges with a nominal molecular weight cut off of 3 and 10 kD. The association of 137Cs, 90Sr, 239Pu and 241Am with different molecular size fractions of the soil solution is discussed in terms of radionuclide bioavailability to cabbage grown in the same three soils. 137Cs and 90Sr were present in low molecular weight forms and as such were mobile in soil and potentially available for uptake by the cabbage. In contrast, a large proportion (61–87%) of the 239Pu and 241Am were associated with colloidal and high molecular weight material and therefore less available for uptake by plant roots. The contribution from low molecular weight species of 239Pu and 241Am to the total activity in soil solution decreased in the order loam > peat ⩾ sand. Association of radionuclides with low molecular weight species of less than 3 kD did not, however, automatically imply availability to plants. In order to improve understanding of the relationship between activity concentrations of radionuclides in soil solution and uptake by plants, further characterisation of the low molecular weight fraction of soil solution is required.

Neurotoxic components in normal serum

Serum neurotoxicity was studied by adding whole or fractionated serum (adult human, adult horse, or newborn calf) to neuron-rich cultures prepared from various regions of embryonic (Days 14–15) rat brain, including spinal cord, ventral mesencephalon, cerebellum, septum, and striatum. Effects of serum were also tested on several types of embryonic non-neuronal cells (skeletal muscle myotubes, cardiac muscle myocytes, and fibroblasts from skin and lung). Serum concentrations of 50% or more killed more than 95% of all neurons within 3 days. Serum concentrations as low as 10% also killed some neurons, especially those from cerebellum. Septal, cerebellar, and spinal cord neurons were more sensitive than striatal or mesencephalic neurons. All the tested non-neuronal cells survived much better than neurons at serum concentrations of 20% or more. Neurotoxicity was present in both fresh (human) and previously frozen (human and animal) sera, and affected both young (4 days in vitro) and older (42 days in vitro) cultures. Neurotoxicity was greatly diminished by heating the serum to 56°C for 30 min. Experiments indicated that serum toxicity was not due to lipoprotein, complement, or tumor necrosis factor. All serum neurotoxicity was retained by an ultrafilter with a nominal molecular weight cutoff of 10 kDa. The profile of neurotoxicity following gel filtration at neutral pH was variable, with high toxicity most consistently observed in fractions with apparent molecular weights exceeding 100 kDa, and variable degrees of toxicity at lower molecular weights.

Effect of membrane structure and protein concentration on the osmotic reflection coefficient

Although there have been a number of important studies of the protein filtration reflection coefficient (or sieving coefficient) for asymmetric ultrafiltration membranes, there have been no corresponding studies of the protein osmotic reflection coefficient and its effect on solvent flux. We have obtained experimental data for the bovine serum albumin osmotic reflection coefficient for asymmetric polyethersulfone membranes with nominal molecular weight cut-offs from 30,000 to 1,000,000. The overall osmotic reflection coefficients for these membranes were smaller than the reflection coefficients of the skin layer due to the substantial diffusive resistance provided by the membrane support structure. The results for the skin layer were in relatively good agreement with available hydrodynamic models, suitably modified to account for the effects of protein adsorption and for the presence of a pore size distribution. The osmotic reflection coefficients decreased with increasing bulk protein concentration, with the concentration dependence somewhat larger than that predicted by available theoretical analyses. The osmotic reflection coefficients were in relatively good agreement with literature values for the corresponding filtration reflection coefficients, with the slightly smaller values for the osmotic reflection coefficients probably reflecting the variation in pore size within the ultrathin skin of these asymmetric membranes.

Adenosine and its nucleotides stimulate proliferation of chick astrocytes and human astrocytoma cells

Aqueous extracts of the brains of 18-day-old white Leghorn chicken embryos contain several substances that stimulate proliferation of primary cultures of chick brain astrocytes. Most of the mitogens are peptides. Purification of one mitogenic fraction was obtained by centrifugation, passage through Amicon Diaflo membranes of nominal molecular weight cutoffs 30, 1 and 0.5 kDa, ion exchange chromatography and reverse phase high performance liquid chromatography (HPLC) using a Deltapak C 18 column. The mitogenic fraction contained to amino acids. On the basis of its behaviour on thin layer chromatography, its ultraviolet absorption spectrum, its 1H and 31P nuclear magnetic resonance spectra and its behaviour on positive and negative ion fast atom bombardment mass spectrometry, the mitogenic material was identified as adenosine-5′-monophosphate (AMP). Other adenosine compounds including adenosine, ADP and ATP also stimulated proliferation of and [ 3H]leucine incorporation into primary cultures of astrocytes. Nitrobenzylthyioinosine (NBTI), an inhibitor of nucleoside transport, did not prevent the stimulation of [ 3H]leucine incorporation into cultured astrocytes. Polyadenylic acid (Poly A), that mimics the effect of adenosine at adenosine receptors, also stimulated proliferation of the astrocytes. The effects of adenosine and Poly A were not inhibited by 1,3-dipropyl-8-(2-amino-4-chlorophenyl)xanthine (PACPX) but were inhibited by 1,3-dipropyl-7-methyl-xanthine (DPMX), indicating that adenosine and Poly A acted at the cell surface, likely through adenosine A 2 receptors. The stimulatory effect of ATP was biphasic. The proliferative effect of low, but not of high, concentrations of ATP were abolished by DPMX. The purinergic P 2 receptor agonist 2-methylthioATP and, at higher concentrations, the P 2y agonist, α,β-methyleneATP also stimulated incorporation of [ 3H]thymidine. These data indicate that high concentrations of ATP stimulate cell proliferation through at a P 2, possibly a P 2y receptor. These results have considerable biological significance. After brain injury, or when cells in brain die or become hypoxic, nucleotides and nucleosides are released from the cells. Their extracellular concentrations can exceed those required to stimulate astrocyte proliferation in vitro. Therefore they may be partly responsible for gliotic changes following cell death in brain.

EFFECT of pH and ENZYMATIC TREATMENT ON MICROFILTRATION and ULTRAFILTRATION of TANGERINE JUICE

ABSTRACTTangerine (Citrus reticulata blanco) juice clarification by crossflow microfiltration and ultrafiltration using polysulphone flat sheet membranes with nominal molecular weight cut off of 25,000, 50,000, 100,000 and 0.1 μm, 0.2 μm pore sizes was studied. the juice was pretreated by polygalacturonase and pH adjustment. the treated juice was clarified with a laboratory scale filtration unit with effective filtration area of 14 cm2. Filtration conditions were transmembrane pressure of 93 to 194 kPa, crossflow velocity of 0.96 to 3.5 m/s and 25°C. Membrane performance was evaluated in terms of volume flux and clarity (% transmittance) of the permeate.Pretreatment of the juice by polygalacturonase and adjustment to pH 2 with HCl resulted in a clearer supernatant than enzyme treatment alone. Maximum flux was obtained with the 0.1 μm microfiltration membrane. Flux increased with transmembrane pressure and crossflow velocity. Flux at 194 kPa and 3.5 m/s was 69 L per square meter per hour. Permeate clarity was better at higher transmembrane pressure and lower velocity, due to the effect of the polarized/fouling layer of solute on the membrane surface, which acted as a secondary “dynamic” filter.

Hindered protein diffusion in asymmetric ultrafiltration membranes with highly constricted pores

Although protein diffusion in constricted pores can play an important role in a variety of membrane processes, there are currently no quantitative data available on the effective protein diffusivity in the highly constricted irregular pores characteristic of asymmetric ultrafiltration membranes. We have obtained data for the hindered diffusion coefficient of bovine serum albumin in polyethersulfone ultrafiltration membranes with nominal molecular weight cut-offs ranging from 50,000 to 1,000,000 using a well-stirred diffusion cell. Results indicate that the highly porous membrane matrix provides nearly 25% of the overall resistance to diffusion in the larger molecular weight cut-off membranes. All measured hindered diffusion coefficients in the ultrathin skin were more than four orders of magnitude smaller than the free solution diffusivity. Protein adsorption in the 1,000,000 molecular weight cut-off membranes attains a full monolayer, thereby constricting the membrane pores and reducing the effective pore size. Comparison of the measured diffusivity with available hydrodynamic models, suitably extended to the asymmetric membranes, indicates that protein adsorption in the 1,000,000 molecular weight cut-off membrane reduces the diffusion coefficient by two orders of magnitude. In contrast, there is minimal adsorption in the very highly constricted pores of the 50,000 molecular weight cut-off membrane. Protein adsorption in the 100,000 and 300,000 molecular weight cut-off membranes attains only a partial monolayer, but this still causes close to a two order of magnitude reduction in diffusivity.

Reverse osmosis membrane characteristics for partitioning triglyceride‐solvent mixtures

AbstractResidual free gossypol in hexane‐extracted cottonseed meal is a frequent concern of the feed industry. It is known that ethanol can efficiently extract the gossypol from cottonseed. However, regeneration of ethanol from ethanol‐rich miscellas by conventional evaporation is costly, due to the high latent heat of ethanol. As an alternative to the evaporative regeneration, reverse osmosis (RO) has been investigated. It was found that commercially available RO membranes which have pore diameter around 20 A‡ (evaluated with deionized water flux) or less perform the necessary partitioning. Among the commercially available RO membranes, cellulose acetate (CA) type membranes with a nominal MWCO (molecular weight cutoff) value between 500 and 1000 were found to be efficient in partitioning the cottonseed triglycerides from the base solvent, but were not chemically compatible with the base solvent. RO membranes made from aromatic polyamide (PA) with MWCO value 1000 were found to have both the chemical stability and the necessary pore characteristics. Experimental results indicated the potential use of RO membranes for the regeneration of ethanol from ethanol miscellas. The required membrane pore characteristics and applicable permeate flux equations are discussed.

Technetium-99 Cycling in Maple Trees

Prior field studies near an old radioactive waste disposal site at Oak Ridge, TN, indicated that following root uptake, metabolism by deciduous trees rendered 99Tc less biogeochemically mobile than expected, based on chemistry of the pertechnetate (TcO-4) anion. Subsequently, the form of technetium (Tc) in maple tree (Acer sp.) sap, leaves, wood and forest leaf litter was characterized using one or more of the following methods: dialysis, physical fractionation, chemical extraction, gel permeation chromatography, enzymatic extraction, or thin layer chromatography (TLC) on silica gel. Chromatography (Sephadex G-25) of TcO-4 incubated in vitro with tree sap showed it to behave similar to TcO-4 anion. When labeled wood and leaf tissues were processed using a tissue homogenizer, 15% and 40%, respectively, of the Tc was solubilized into phosphate buffer. Most (65% to 80%) of the solubilized Tc passing a 0.45-micron filter also passed through an ultrafiltration membrane with a nominal molecular weight cutoff of 10,000 atomic mass units (amu). A majority (72% to 80%) of the Tc in wood could be chemically removed by successive extractions with ethanol, water and weak mineral acid. These same extractants removed only 23% to 31% of the Tc from maple leaves or forest floor leaf litter. Most of the Tc in leaves and leaf litter was removed only by strongly alkaline reagents typically used to release structural polysaccharides (hemicelluloses) from plant tissues. Chromatography (Sephadex G-25) of the ethanol-water extract from wood and the alkaline extract from leaves demonstrated that Tc in these extracts was not principally TcO-4 but was complexed with molecules greater than 1000 amu. Incubations of leaf and wood homogenates with protease approximately doubled the amount of Tc released from contaminated tissues. Ultrafiltration of protease-solubilized Tc from leaves and wood showed that 40% and 93%, respectively, of the Tc was less than 10,000 amu. TLC of the less than 10,000 amu fraction indicated the presence of TcO-4 in wood but not in leaves. In the leaf, TcO-4 is converted to less soluble forms apparently associated with structural components of leaf cell walls. This conversion explains why 99Tc is not easily leached by rainfall from tree foliage and why 99Tc appears to accumulate in forest floor leaf litter layers at the Oak Ridge study site.

Determination of polyacrylamides in coal washery effluents by ultrafiltration/size-exclusion chromatography-ultraviolet detection techniques

The use of a combined technique of ultrafiltration and aqueous size-exclusion high-performance liquid chromatography-UV detection for monitoring trace levels of residual polyacrylamide flocculants in coal washery process water is described. Flocculants of both anionic and non-ionic types in effluents are analyzed by chromatography on a TSK 5000 PW type hydrophilic and semirigid porous polymer gel with 0.05 M Na/sub 2/SO/sub 4/ in water as the mobile phase and by UV detection at 208-nm wavelength for detection. Precision studies gave a relative standard deviation of 5.8% and a precision of 2.2% at the 95% confidence level in the concentration range of 20 ppm. The lower limit of detection for the method is 1.0 ..mu..g. Prior to chromatography, fractionation and concentration of the polyacrylamide in effluents are achieved by ultrafiltration with a hollow fiber cartridge having a nominal molecular weight cutoff of 100,000, and recoveries are determined by spiking studies. The application of the techniques for the analysis of residual flocculant in a coal washery thickener feed effluent sample is described.

Solid-state 13C NMR studies of dissolved organic matter in pore waters from different depositional environments

Dissolved organic matter (DOM) in pore waters from sediments of a number of different depositional environments was isolated by ultrafiltration using membranes with a nominal molecular weight cutoff of 500. This > 500 molecular weight DOM represents 70–98% of the total DOM in these pore waters. We determined the gross chemical structure of this material using both solid-state 13C nuclear magnetic resonance spectroscopy and elemental analysis. Our results show that the DOM in these pore waters appears to exist as two major types: one type dominated by carbohydrates and paraffinic structures and the second dominated by paraffinic and aromatic structures. We suggest that the dominance of one or the other structural type of DOM in the pore water depends on the relative oxidizing/reducing nature of the sediments as well as the source of the detrital organic matter. Under dominantly anaerobic conditions carbohydrates in the sediments are degraded by bacteria and accumulate in the pore water as DOM. However, little or no degradation of lignin occurs under these conditions. In contrast, sediments thought to be predominantly aerobic in character have DOM with diminished carbohydrate and enhanced aromatic character. The aromatic structures in the DOM from these sediments are thought to arise from the degradation of lignin. The large amounts of paraffinic structures in both types of DOM may be due to the degradation of unidentified paraffinic materials in algal or bacterial remains.

Heat-Unstable Proteins in Grape Juice and Wine. II. Characterization and Removal by Ultrafiltration

White Riesling and Gewürztraminer wine and juice were ultrafiltered with Romicon and Millipore systems operated with membranes of nominal molecular weight cut-offs (MWCO) of 10 000 to 100 000 daltons. A progressive increase in membrane retention of soluble protein was observed with decreasing MWCO, up to 99% of the protein in wine being retained with membranes of 10 000-dalton MWCO. In the order of 3 to 20 mg/L protein frequently remained in ultrafiltration (UF) wine permeates; this correlated with the periodic detection of heat instability and of a low bentonite requirement for protein stability as determined by sensitive heat testing. Protein stability could be obtained with MWCO of 10 000 and 30 000; however when not obtained, reductions in the order of 80% to 95% in the bentonite requirement were achieved. The nature of unstable proteins and their removal by UF was further characterized by determining protein molecular weights (MW), isoelectric points (pl), and glycoproteins by lithium dodecyl sulfate polyacrylamide gel electrophoresis (LDS PAGE), two-dimensional isoelectric focusing-lithium dodecyl sulfate (IF-LDS) gel electrophoresis, silver staining, and protein blotting. Protein stabilization of wines by UF is similar to that by bentonite fining in that it is not until the lower MW (12 600 - 30 000) and lower pl (4.1 - 5.8) fractions and glycoproteins are removed that wines become protein stabilized to heat testing. Protein fractions in juices and wines behaved differently with UF. UF membranes were more effective in retaining wine proteins than juice proteins. Membranes were capable of retaining all glycoproteins in wines but not in juices. UF juices were more susceptible to heat-induced haze formation than UF wines.

Nutritional factors affecting the synthesis of an antiphagocytic factor by group E streptococci.

Effects of components of the cultural medium on formation of a group E streptococcal antiphagocytic factor (APF), as detected by an indirect bactericidal test, were studied. Bovine serum albumin (BSA) replaced serum in promoting synthesis of APF in a chemically defined medium (CDM), Todd--Hewitt broth (THB), or tryptose phosphate broth ( TPB ). Stimulatory factors in BSA were not retained by diafiltration membranes of nominal molecular weight cutoff limits of 10 000 or greater. Citrate, lactate, pyruvate, or oleate, often found in BSA, could not replace BSA in stimulating synthesis of APF. Cells cultured in THB were more resistant to phagocytosis by porcine leukocytes than those grown in CDM or TPB , and the addition of varying amounts of THB to CDM stimulated a measurable response in synthesis of APF. Specific substrates caused different rates of APF synthesis; in decreasing order of effectiveness were glucose or mannose, sucrose, fructose, and trehalose. Proteolytic activity, which might cause the production of phagocyte-sensitive cells by destroying APF activity during culture, was not detectable in significant amounts in subcultures of the age employed in bactericidal tests.