Isoelectric Point Of BSA Research Articles

PH-dependent structure, pattern and hysteresis behaviour of lipid (DMPA)-protein (BSA) monolayer complex

Understanding lipid-protein interactions in model membranes is a challenging task. Limited information exist to-date regarding the relative influence of hydrophobic and electrostatic forces on the organization of proteins inside model membranes, while these forces determine the structure of lipid-protein complexes. We measured the surface pressure (π) - molecular area (A) isotherm cycles of protein (BSA) – lipid (DMPA) mixed monolayers below and above the isoelectric point of BSA (≈ 4.8). At pH ≈ 4.0, below the isoelectric point, BSA is positively charged, and exposes few hydrophobic groups at its surface, compression-decompression isotherms show a nearly reversible hysteresis. At pH ≈ 7.0, above the isoelectric point, BSA is negatively charged and more hydrophobic. At this pH, compression-decompression isotherms show an irreversible hysteresis. This behaviour indicates that the deformation of BSA molecules under pressure is reversible below the isoelectric point, while it becomes irreversible above it. X-ray reflectivity studies for protein-lipid mixed monolayers show that BSA molecules move from the zone close to water and near the lipid polar heads toward the zone occupied by their hydrocarbon tails s when surface pressure increases. Mostly the surface pressure in combinations with hydrophobic and electrostatic interactions is responsible for such structural modifications.

Modification of hysteresis behaviors of protein monolayer and the corresponding structures with the variation of protein surface charges

Successive compression-decompression cycles of the surface pressure (π) − specific molecular area (A) isotherms of protein (BSA) monolayers show that reversible hysteresis persists if the protein molecules contain effective positive or negative surface charges. However, for neutral condition, i.e., close to the isoelectric point of the protein, irreversibility in the hysteresis behaviour dominates. Out-of-plane structures obtained from the X-ray reflectivity analysis suggest that at lower surface pressure monomolecular layer of BSA is formed on the water surface. With increasing surface pressure, molecules start to lift-up from the water surface in such a way that semi-major axis makes an angle with the water surface. Depending on the surface pressure and surface charge of BSA, monomolecular or bimolecular layer of tilted BSA molecules is formed on the water surface, however, formation of bimolecular layer is observed when the pH is relatively closer to the BSA isoelectric point. After complete decompression, tilted monomolecular or bimolecular structures again transform into monomolecular layer as evidenced from the structural analysis of the films deposited at lower surface pressures in the second compression, however, structural hysteresis varies depending upon the subphase pH or protein surface charge. Structures obtained from the films deposited at first and second compressions at lower pressure implies that although structural dissimilarity is present but structural hysteresis is only present near the isoelectric point of BSA and becomes negligible below and above that pH. Competitive electrostatic and van der Waals interactions are responsible for such hysteresis behaviours and structural modifications.

Control of protein (BSA) fouling in RO system by antiscalants

The control of protein (bovine serum albumin, BSA) fouling by antiscalants was investigated in a bench-scale crossflow reverse osmosis (RO) system. Two antiscalants, polyaspartic acid (PASP) and an organophosphorus compound (LB-0100), were tested. The results indicated that BSA fouling could be greatly reduced by properly dosing antiscalants. The inhibition efficiency increased with PASP concentration but decreased when overdosing. LB-0100 was found to be less effective than PASP, and would greatly aggravate RO membrane fouling when overdosing. In the presence of PASP, Ca 2+ had positive impact on fouling control within a certain concentration range and the foulant particle size decreased. This may be due to the possible formation of a water-soluble and highly stable complex BSA–Ca–PASP via Ca 2+ bridging and not due to the electrostatic repulsion as measured by zeta potential. BSA fouling decreased at higher solution pH above the iso-electric point of BSA, lower initial permeate flux, and higher crossflow velocity in both the absence and presence of PASP. However, the fouling behaviors became less susceptible to these parameters in the presence of PASP. The effect of feed temperature in the presence of PASP was found to be opposite to that in the absence of PASP.

Streaming potential sensing in paper-based microfluidic channels

Streaming potential measurements detected the presence of adsorbed polyvinylamine or potassium polyvinylsulfate in paper-based microfluidic devices. Capillary driven flow in filter paper induced measurable potentials in the range −80 to +80 mV. The magnitude and polarity of the measured potentials were sensitive to the presence of adsorbed polymer. In a second example, paper treated with BSA gave a positive streaming potential at pH 3.7, below the isoelectric point of BSA, and a negative potential at high pH. We propose that streaming potential may provide an electronic interface for paper-based biosensors.

The role of hydrodynamic conditions and solution chemistry on protein fouling during ultrafiltration

This study investigates the effect of hydrodynamic conditions and solution chemistry on protein fouling during ultrafiltration. Drastic flux reduction was observed at high initial flux and/or low cross-flow velocity. A limiting flux existed during BSA filtration, beyond which membrane flux cannot be sustained. Further increase in pressure over the limiting value did not enhance the stable flux. The rate and extent of BSA fouling were also strongly dependent on the feedwater composition, such as BSA concentration, pH, and ionic strength. Foulant concentration had no effect on the stable flux, although the rate approaching to the stable flux increased proportionally with increasing foulant concentration. Fouling was most severe at the isoelectric point of BSA (pH 4.7), where the electrostatic repulsion between foulant molecules is negligible. Membrane fouling became less severe at pHs away from the isoelectric point. Increasing ionic strength at pH 3.0 promoted severe fouling likely due to electric double layer (EDL) compression. On the other hand, the flux behavior was insensitive to salt concentration at pH 4.7 due to the lack of electrostatic interaction. At a solution pH of 5.8, effect of ionic strength on long-term flux behavior was directly opposite to that on the transient behavior. While the long-term flux was lower at higher ionic strength due to EDL compression, the transient behavior was also affected by the BSA retention of the membrane.

Influence of pH and salt concentration on the cross-flow microfiltration of BSA through a ceramic membrane

In this paper, the influence of pH in the 4–8 interval and NaCl concentration up to 25 mM on the cross-flow microfiltration of BSA was investigated. A tubular ceramic membrane with a pore size of 0.14 μm was employed and its point of zero charge was calculated. The evolution of permeate flow and BSA transmission with time was determined at 45 °C, a cross-flow velocity of 3.5 m/s and a transmembrane pressure of 100 kPa. The curves of permeate flow were explained according to the resistances in series model. Maximum protein transmission was obtained at the isoelectric point of BSA (4.9), with significant transmission also at the point of zero charge of the membrane and null transmission at pH 4 and 8. The highest permeate flow was observed at pH 7 and the lowest at 4.9. Finally, the addition of salt resulted to some extent in an improvement of both protein transmission and permeate flow.

Solute rejection in the presence of a deposited layer during ultrafiltration

During ultrafiltration deposited layers are often formed on the membrane surface. These layers not only reduce the volumetric flux through the membrane, but also may influence the rejection of other solutes in the feed. In the present paper we will show that besides an increase in the rejection, a decrease in rejection may also occur, which can completely alter the aimed selectivity of the separation process. The influence of deposited layers has been studied experimentally by two types of depositing components: silica sol and the protein BSA. In the presence of a relatively open silica deposit a strong drop in the rejection of PEG and dextran was found compared to the rejection on a clean membrane. For thick deposit layers the rejection even decreased to zero, thus resulting in a total permeation of a normally partially rejected solute. On the other hand an increase in PEG rejection occurred in the presence of a BSA deposit. Due to the compressibility of the protein deposit the highest rejections were measured at the highest pressures. The effects were the most pronounced at the isoelectric point of BSA. A model is presented to describe the underlying phenomena.

Dynamic analysis of irreversible adsorption of protein on porous polymer resins as studied by pulse injection method

Irreversible adsorption of bovine serum albumin onto porous polymer resins is examined by a pulse injection method. The experimental results are theoretically analyzed by a model based on the assumption that there exist three kinds of binding sites with different binding rates, which are considered to exist in the vicinity of the outer periphery surface, the inner surface of macropore, and the micropore, or center part, of particles. The three kinds of adsorption rates are also evaluated by a batch method and are nearly equal to the corresponding kinetic parameters by this method. The amount of BSA bound irreversibly to the resins is independent of the protein concentration and the flow rate examined, which suggests that protein molecules penetrate into pores of resins and occupy almost all the effective binding sites in the resins. The total amount of bound BSA shows a pH dependence with a maximum near the isoelectric point of BSA, and the amount of BSA bound at the slowest rate is most largely influenced by pH.