Bovine serum albumin partitioning in an aqueous two-phase system: effect of pH and sodium chloride concentration

The partitioning of bovine serum albumin (BSA) in a polyethylene glycol 3350 (8% w/w)-dextran 37 500 (6% w/w)-0.05 M phosphate aqueous two-phase was investigated at different pHs, at varying concentrations of sodium chloride at 20 degrees C. The effect of NaCl concentration on the partition coefficient of BSA was studied for the PEG-dx systems with initial pH values of 4.2, 5.0, 7.0, 9.0, and 9.8. The NaCl concentrations in the phase systems with constant pH value were 0.06, 0.1, 0.2, 0.3, and 0.34 M. It was observed that the BSA partition coefficient decreased at concentrations smaller than 0.2 M NaCl and increased at concentrations greater than 0.2 M NaCl for all systems with initial pHs of 4.2, 5.0, 7.0, 9.0, and 9.8. It was also seen that the partition coefficient of BSA decreased as the pH of the aqueous two-phase systems increased at any NaCl salt concentration studied.

Phase behavior and protein partitioning in aqueous two-phase systems of cationic--anionic surfactant mixtures

Cationic-anionic surfactant mixtures can form aqueous two-phase systems. Such aqueous surfactant two-phase systems (ASTP systems) can be used for separation and purification of biomaterials. In this work we investigated the phase behavior and the partitioning of BSA and lysozyme in the ASTP system formed by mixtures of dodecyltriethylammonium bromide and sodium dodecylsulfate (SDS). The pseudo ternary phase diagram of these mixtures at low total surfactant concentrations contains two narrow two-phase regions, which represent two kinds of different ASTP systems formed when cationic and anionic surfactants are in excess, respectively (called ASTP-C and ASTP-A). The phase separation is associative, one phase is surfactant-rich, and the other phase is surfactant-depleted. Mechanisms behind the phase behavior are discussed. The phase behavior, especially phase separation time and phase volume ratio, is strongly influenced by total concentration and molar ratio of mixed surfactants. The effect of molar ratio is strong, which enables one to get desired phase systems also at very low total concentration by tuning the molar ratio of the surfactants. It was shown that the marked differences of surfactant concentration between the phases makes proteins distribute with different partitioning coefficients. The charges on the micellar surface, which can be adjusted by tuning the molar ratio of cationic surfactants to anionic surfactants, enhance the selectivity of protein partitioning by electrostatic effects. At pH 7.1, in the ASTP-C systems, negatively charged BSA is concentrated in the surfactant-rich phase and positively charged lysozyme in the surfactant-depleted phase, while in ASTP-A systems, a totally opposite partitioning was observed. It was shown that lysozyme could retain activity in ASTP systems.

Partitioning of whey proteins, bovine serum albumin and porcine insulin in aqueous two-phase systems

Partitioning of the proteins from cheese whey, bovine serum albumin and porcine insulin were analysed using aqueous two-phase systems (ATPS) prepared with PEG-phosphate, PEG-citrate and PEG-maltodextrin (MD). Proteins were quantified through one of the following methods: FPLC, Bradford and spectrophotometry at 280 nm. Results showed that whey proteins partitioned unevenly on the phases of the systems used, with alpha-lactoalbumin (alpha-La) concentrated in the upper phase and beta-lactoglobulin (beta-Lg) in the lower. Albumin in PEG-MD systems concentrated in the MD-rich lower phase. Porcine insulin showed great affinity with the PEG-rich phase, its partition coefficient was always over 10 and increases with PEG molecular mass.

Partitioning of bovine serum albumin in an aqueous two-phase system: optimization of partition coefficient

Partitioning of proteins in aqueous two-phase systems has been shown to provide a powerful method for separating and purifying mixtures of biomolecules by extraction. There are many factors which influence the partition coefficient K, the ratio of biomolecule concentration in top phase to that in the bottom phase, in aqueous two-phase systems. In this work, the partition behavior of pure bovine serum albumin in aqueous two-phase systems was investigated in order to see the effects of changes in phase properties on the partition coefficient K. pH and concentration of NaCl salt were found to be the factors having influence on K. Optimal conditions of these factors were obtained using the Box-Wilson experimental design. The optimum value of K was found as 0.018 when NaCl concentration, and pH were 0.0195 M and 8.9, respectively, for a phase system composed of 8% (w/w) polyethylene glycol 3350-6% (w/w) dextran 37 500-0.05 M phosphate at 20 degrees C.

Application of multichannel flow electrophoresis to separation of biomolecules: a survey

Multichannel flow electrophoresis (MFE) is a newly developed method for continuous separation of biological products at a preparative scale, In this short survey, the application of MFE in the separation of proteins, enzymes and antibodies are overviewed.

Foam fractionation of binary mixtures of lysozyme and albumin

A nitrogen gas-based foam fractionation method was employed to separate model proteins, bovine serum albumin (BSA) and hen egg white lysozyme, from each other. Fractionation was characterized by the separation ratio and by recovery of proteins in the retentate as a function of the nominal pore size of the gas dispersion frit and solution conditions (pH and ionic strength). For binary mixtures of the proteins at pH 7.4, and ionic strength (mu) of 0.18 M, the recovery of lysozyme and the separation ratio were both dependent on the frit size employed to generate the foam. At low ionic strength (mu = 0.01 M), separation was only somewhat greater with the small pore size frits, although at values significantly lower than those found for high ionic strength. The diminished separations appear to be due to the only slight changes in recoveries observed for BSA and lysozyme.%Separation ratios of lysozyme from BSA in solutions either of high or low ionic strength were maximal at pH values equal to or less than the isoelectric point (pI) of BSA. Separation ratios were lower when foaming was carried out under low compared with high ionic strength. The recovery of lysozyme was enhanced by foaming from solutions of low pH and high ionic strength. Recoveries of BSA were greatest when the molecule was negatively charged. Electrical interactions between the positively charged lysozyme and negatively charged BSA may explain the diminished separation ratios and enhanced recoveries. Enzyme activity studies of lysozyme remaining in the retentate showed no change from prefoam activity.

The effect of column verticality on separation efficiency in expanded bed adsorption

The effect of column verticality on liquid dispersion and separation efficiency in expanded bed adsorption columns was investigated using 1 and 5 cm diameter columns. Column misalignment of only 0.15 degree resulted in the reduction of the Bodenstein number from 140 to 50 for the 1 cm dia. column and from 75 to 45 for the 5 cm dia. column. This degree of misalignment was not detectable by visual assessment of adsorbent particle movement within the column. Depending on the relative importance of transport limitations, kinetic limitations and dispersion to any specific separation, this increase in dispersion with column alignment can significantly affect separation efficiency. Pure protein breakthrough profiles resulting from the application of bovine serum albumin onto STREAMLINE Q XL demonstrated that, at 10% breakthrough, 7.8% more protein could be applied to a vertical 1 cm dia. column compared to the same column misaligned by 0.15 degree. When an unclarified yeast homogenate was applied to a 1 cm dia. vertical column packed with STREAMLINE DEAE, 10% breakthrough of glucose-6-phosphate dehydrogenase (G6PDH) corresponded to a load 55% greater compared to the same column aligned 0.185 degree off-vertical. The G6PDH breakthrough curves for vertical and 0.15 degree off-vertical runs performed using a 5 cm column were essentially indistinguishable.

Preparative electrochromatography of proteins in various types of porous media

The performance of commercial and enzymatically modified size-exclusion (SE) gels in electrochromatography was compared for preparative protein separations. Dextran and agarose-based SE gels were subjected to enzymatic digestion under mild conditions. This treatment partially hydrolyzed the gel matrix modifying its pore size distribution. Enzymatic treatment of agarose-based SE gels was found to increase the resolution of the separation. Successful separation of preparative amounts of the A and B forms of beta-lactoglobulin (difference in electrophoretic mobility of 8.5%) was achieved with a high degree of purity using agarose-based SE gels. The four major whey proteins, beta-lactoglobulin, alpha-lactalbumin, BSA and immunoglobulins, were purified from an acid whey preparation. The degree of retention of a protein in electrochromatography followed their free-solution electrophoretic mobility (mu) when the protein was able to enter the gel pores and the ratio of diffusion/mu when the protein was excluded.

[Effect of treated with weak magnetic field aqueous salt solutions on the intrinsic fluorescence of bovine serum albumin. Isolation from solutions and partial characterization of the biologically active fluorescing fraction]

It was shown that water with additions of Ca2+, Na+, K+ and Cl- ions preliminarily treated with weak combined constant (42 microT) and low-frequency alternating (0.06 microT) magnetic fields affects the intrinsic fluorescence of bovine serum albumin, the magnitude of the effect being dependent on the frequency of the alternating field and ionic composition of the aqueous salt solution. A practically complete transfer of the effect through a small portion of the solution treated with magnetic fields was revealed. It was also found that after magnetic treatment, the solution contains a rather large (molecular mass 700-900 D) and stable molecular associate, which possesses, at least partially, the properties and characteristics inherent in the whole solution that were as acquired as a result of magnetic treatment.

Electrophoretic transfer of proteins across polyacrylamide membranes

The electrophoretic transfer of purified proteins has been examined in a Gradiflow "Babyflow BF100" unit. A number of factors affect protein separation within this preparative electrophoresis system. We established that the rate of protein transfer was proportional to the applied voltage. The transfer is slowest at the isoelectric point (pI) and increased the further away the pH was from the pI of the protein. Protein transfer was found to be independent of the ionic strength of the buffer, for buffers that excluded the addition of strong acids or strong bases or sodium chloride. Transfer decreased as the pore size of the membrane decreased. Finally, transfer was inhibited at high salt concentrations in the protein solution, but remained unaffected when urea and non-ionic detergents were added to the solution. To increase the speed of protein separations, buffers with low conductivity should be used. A pH for the optimal separation should be selected on the basis of the relative pI and size of the target proteins and that of the major contaminants.

Purification of protein and recycling of polymers in a new aqueous two-phase system using two thermoseparating polymers

In this study we present a new aqueous two-phase system where both polymers are thermoseparating. In this system it is possible to recycle both polymers by temperature induced phase separation, which is an improvement of the aqueous two-phase system previously reported where one of the polymers was thermoseparating and the other polymer was dextran or a starch derivative. The polymers used in this work are EO50PO50, a random copolymer of 50% ethylene oxide (EO) and 50% propylene oxide (PO), and a hydrophobically modified random copolymer of EO and PO with aliphatic C14H29-groups coupled to each end of the polymer (HM-EOPO). In water solution both polymers will phase separate above a critical temperature (cloud point for EO50PO50 50 degrees C, HM-EOPO, 14 degrees C) and this will for both polymers lead to formation of an upper water phase and a lower polymer enriched phase. When EO50PO50 and HM-EOPO are mixed in water, the solution will separate in two phases above a certain concentration i.e. an aqueous two-phase system is formed analogous to poly(ethylene glycol) (PEG)/dextran system. The partitioning of three proteins, bovine serum albumin, lysozyme and apolipoprotein A-1, has been studied in the EO50PO50/HM-EOPO system and how the partitioning is affected by salt additions. Protein partitioning is affected by salts in similar way as in traditional PEG/dextran system. Recombinant apolipoprotein A-1 has been purified from a cell free E. coli fermentation solution. Protein concentrations of 20 and 63 mg/ml were used, and the target protein could be concentrated in the HM-EOPO phase with purification factors of 6.6 and 7.3 giving the yields 66 and 45%, respectively. Recycling of both copolymers by thermoseparation was investigated. In protein free systems 73 and 97.5% of the EO50PO50 and HM-EOPO polymer could be recycled respectively. Both polymers were recycled after aqueous two-phase extraction of apolipoprotein A-1 from a cell free E. coli fermentation solution. Apolipoprotein A-1 was extracted to the HM-EOPO phase with contaminating proteins in the EO50PO50 phase. The yield (78%) and purification factor (5.5) of apolipoprotein A-1 was constant during three polymer recyclings. This new phase system based on two thermoseparating polymers is of great interest in large scale extractions where polymer recycling is of increasing importance.

Thermoseparating water/polymer system: a novel one-polymer aqueous two-phase system for protein purification

In this study we show that proteins can be partitioned and separated in a novel aqueous two-phase system composed of only one polymer in water solution. This system represents an attractive alternative to traditional two-phase systems which uses either two polymers (e.g., PEG/dextran) or one polymer in high-salt concentration (e.g., PEG/salt). The polymer in the new system is a linear random copolymer composed of ethylene oxide and propylene oxide groups which has been hydrophobically modified with myristyl groups (C(14)H(29)) at both ends (HM-EOPO). This polymer thermoseparates in water, with a cloud point at 14 degrees C. The HM-EOPO polymer forms an aqueous two-phase system with a top phase composed of almost 100% water and a bottom phase composed of 5-9% HM-EOPO in water when separated at 17-30 degrees C. The copolymer is self-associating and forms micellar-like structures with a CMC at 12 microM (0.01%). The partitioning behavior of three proteins (lysozyme, bovine serum albumin, and apolipoprotein A-1) in water/HM-EOPO two-phase systems has been studied, as well as the effect of various ions, pH, and temperature on protein partitioning. The amphiphilic protein apolipoprotein A-1 was strongly partitioned to the HM-EOPO-rich phase within a broad-temperature range. The partitioning of hydrophobic proteins can be directed with addition of salt. Below the isoelectric point (pI) BSA was partitioned to the HM-EOPO-rich phase and above the pI to the water phase when NaClO(4)was added to the system. Lysozyme was directed to the HM-EOPO phase with NaClO(4), and to the water phase with Na-phosphate. The possibility to direct protein partitioning between water and copolymer phases shows that this system can be used for protein separations. This was tested on purification of apolipoprotein A-1 from human plasma and Escherichia coli extract. Apolipoprotein A-1 could be recovered in the HM-EOPO-rich phase and the majority of contaminating proteins in the water phase. By adding a new water/buffer phase at higher pH and with 100 mM NaClO(4), and raising the temperature for separation, the apolipoprotein A-1 could be back-extracted from the HM-EOPO phase into the new water phase. This novel system has a strong potential for use in biotechnical extractions as it uses only one polymer and can be operated at moderate temperatures and salt concentrations and furthermore, the copolymer can be recovered.

Isolation of bovine serum albumin fragment P-9 and P-9-mediated fusion of small unilamellar vesicles

Fusion peptide P-9 was isolated from bovine serum albumin by controlled pepsin degradation in the presence of caprylic acid, followed by Sephadex G-75 gel filtration and ion-exchange chromatography of CM-cellulose. By this procedure, P-9 could be strictly separated from peptic fragment P-Phe, which has a molecular weight close to that of P-9. P-Phe has no fusogenic activity. The addition of P-9 to phosphatidylcholine (PC) liposomes containing cholesterol (Chol) gave rise to an increase of absorption intensity at around pH 4.0. The increase of turbidity by P-9 addition did not decrease with increasing pH, indicating P-9-mediated fusion of PC liposomes. The extent of the fusion of PC liposomes was strongly dependent on the PC chain length and temperature. The membrane fluidity close to the polar head groups of the fatty acyl chains of PC affected markedly the extent of P-9-mediated liposome fusion. However, there was no correlation between membrane fluidity near the hydrophobic end of the fatty acyl chains and the extent of liposome fusion. The rate of liposome fusion was dependent on both lipid composition and PC chain length. These results suggest that a contact or an interaction of P-9 with liposomal membrane occurs in the rigid regions. The character of the membrane-water interface region in the liposome controls a triggering effect for P-9-mediated fusion.

An integrated process for biomolecule isolation and purification

Biomolecule isolation and purification from a fermentation broth usually involve centrifugation, filtration, adsorption, and chromatography steps. Each step contributes to the product cost and product loss. In this research, a cyclic process integrating commercially available ultrafiltration membranes and chromatographic resin beads was developed to achieve the same goal in one device. The device consisted of ion exchange beads on the shell side of a hollow fiber ultrafiltration module. Loading of proteins on the stationary phase on the shell side was carried out for a period of 5-20 min from the permeate on the shell side produced from tube-side feed in ultrafiltration. The eluent was then introduced either from the shell-side inlet or tube-side inlet; the chromatographic fractions were collected from the shell-side outlet. The column was regenerated/washed next to start a new cycle. Systems studied in this cyclic process include the following binary mixtures: myoglobin and beta-lactoglobulin; hemoglobin and bovine serum albumin; and myoglobin and alpha-lactalbumin. Excellent resolutions of the proteins were obtained. A yeast-based cellular suspension containing a mixture of myoglobin and alpha-lactalbumin was also applied to this device. The target proteins were recovered and purified successfully. The cyclic process-based device integrates clarification, concentration, and chromatographic purification of biomolecules and is suitable for both extracellular and intracellular products.

HPCPC separation of proteins using polyethylene glycol-potassium phosphate aqueous two-phase

High Performance Centrifugal Partition Chromatography (HPCPC) is a practical and suitable method, particularly on the preparative scale, for the separation of biomolecules such as proteins, enzymes, etc. Aqueous two-phase system is also very attractive for the isolation of biomolecules. Aqueous polymer phase system composed of polyethylene glycol 6000-potassium phosphate has been used for the countercurrent chromatographic separation of bovine serum albumin (BSA) and lysozyme using HPCPC. The separation of BSA and lysozyme under various conditions such as various flow rates, rotational speeds, pH of the solvent, and the retention of stationary phase has been studied in the present investigation. The baseline separation of BSA and lysozyme has been also observed. The results of this study demonstrate that HPCPC is useful for separation of proteins with aqueous two-phase systems.

Affinity extraction of BSA with reversed micellar system composed of unbound Cibacron Blue

Affinity Cibacron Blue 3GA (CB) dye in aqueous phase was directly transferred to the reversed micelles due to electrostatic interaction between anionic CB and cationic cetyltrimethylammonium bromide (CTAB). The bovine serum albumin (BSA) transfer to the reverse micelles increases significantly in a wide range of pH by the addition of a small amount of CB ( approximately 1.0-7.0% of the total surfactant concentration) to the aqueous phase. For pH < pI, the selectivity can be significantly improved with the presence of affinity CB because no BSA was extracted in the absence of CB. For backward extraction of BSA from the micellar phase with stripping aqueous solution, the addition of 2-propanol to the aqueous phase can recover almost all BSA (98.5%) extracted into the reverse micelles.

Separation of bovine serum albumin and its monoclonal antibody from their immunocomplexes by sodium dodecyl sulfate-capillary gel electrophoresis and its application in capillary electrophoresis-based immunoassay

A non-competitive immunoassay was performed by sodium dodecyl sulfate-capillary gel electrophoresis with UV detection using bovine serum albumin (BSA) and monoclonal anti-BSA. BSA, anti-BSA and their immunocomplexes were well resolved under non-denaturing conditions. A linear calibration curve was obtained and can be used for the quantification of anti-BSA. The limit of detection of anti-BSA was 0.1 microM under the present conditions. Compared with capillary zone electrophoresis, we believed that this method has the potential to be used as a more general format for performing capillary electrophoresis-based immunoassay of medium- and large-sized analytes.

Study of enantioselective interactions between chiral drugs and serum albumin by capillary electrophoresis

The separation of the enantiomers of three basic drugs, i.e., ofloxacin, propranolol and verapamil, was achieved by affinity capillary electrophoresis (ACE), with human serum albumin (HSA) and bovine serum albumin (BSA) as chiral selectors in phosphate buffer at pH 7.4. Ofloxacin was only separated in the presence of BSA, and verapamil only with HSA, while propranolol was separated with either HSA or BSA. The effects of protein concentration and column wall adsorption on the degree of separation were investigated. Two displacers, ketoprofen and warfarin, respectively, when added to the protein containing buffer, both showed significant effects on the separation behavior. From these data it was argued that verapamil may bind to HSA at both locations known, the warfarin binding site (I) and the ketoprofen binding site (II). While with BSA, binding of ofloxacin may also occur at site I, the preferential binding site for propanolol remains controversial. A drug-drug interaction between propranolol and ketoprofen due to opposite charges was concluded from the increase in migration time in BSA solution. The unbound concentration of verapamil enantiomers in solution in the presence of HSA, as estimated from CD-modified capillary zone electrophoresis, was triggered not only by the HSA concentration but also by the coadditive concentration.

[Hydrophobic membrane chromatography for fast purification of biological macromolecules]

Cellulose membrane bonded with four commonly used hydrophobic groups, octyl, butyl, phenyl and polyethylene glycol was first investigated for their binding and purification characteristics of protein and enzyme with octyl- and phenyl-Sepharose CL-4 B as controls. Hydrophobic membranes bound BSA effectively by hydrophobic interaction in high salt solution. Their binding capacities were not notably affected by significantly increasing the flow mass rate or decreasing the mass concentration of protein solution, but were much lower than those of octyl- and phenyl-Sepharose CL-4B. 11.8 fold of purification with an approximately 100% recovery of bovine liver catalase was achieved by step gradient elution on the phenyl cellulose membrane cartridge in a single step in only ten mins or a little more. Increase of the flow mass rate had no effect on the purification of catalase, however, the processing time was shortened greatly. Hydrophobic membrane chromatography here reported exibits a potential of fast processing of the protein solution in large volume with low mass concentration of the target protein, such as genetic engineering culture solution.

Hydrophilic and cationic latex particles for the specific extraction of nucleic acids

The adsorption of BSA and RNA onto hydrophilic and thermosensitive poly(N-isopropyl-acrylamide) (NIPAM) latex particles was described as a function of pH, ionic strength and temperature. The hydrogel poly(NIPAM) latex was synthesized by precipitation polymerization in the presence of a cationic amino-containing monomer. The latex obtained was characterized in terms of particle size, and electrophoretic mobility as a function of pertinent variables: pH, temperature and ionic strength. The adsorption of BSA onto the latex was investigated to identify the conditions at which the adsorbed amount of BSA was negligible. The adsorption of RNA was studied to establish the conditions which give rise to maximal adsorption of RNA. In order to favor the desorption of RNA, desorption was investigated by changing the pH, ionic strength, and temperature. The adsorption of BSA was found to be lower at 20 than at 40 degrees C. However, the adsorption of RNA is drastically affected by the pH and the ionic strength of the medium. Maximal adsorbed amounts were obtained at acidic pH, 20 degrees C, and low ionic strength. The adsorption is shown to decrease when the pH, temperature and ionic strength increase, implying that the adsorption was mainly governed by electrostatic interactions. Maximal release of RNA molecules was obtained at high ionic strength and basic pH.

Aqueous two-phase systems containing self-associating block copolymers. Partitioning of hydrophilic and hydrophobic biomolecules

A series of proteins and one membrane-bound peptide have been partitioned in aqueous two-phase systems consisting of micelle-forming block copolymers from the family of Pluronic block copolymers as one polymer component and dextran T500 as the other component. The Pluronic molecule is a triblock copolymer of the type PEO-PPO-PEO, where PEO and PPO are poly(ethylene oxide) and poly(propylene oxide), respectively. Two different Pluronic copolymers were used, P105 and F68, and the phase diagrams were determined at 30 degrees C for these polymer systems. Since the temperature is an important parameter in Pluronic systems (the block copolymers form micellar-like aggregates at higher temperatures) the partitioning experiments were performed at 5 and 30 degrees C, to explore the effect of temperature-triggered micellization on the partitioning behaviour. The temperatures correspond to the unimeric (single Pluronic chain) and the micellar states of the P105 polymer at the concentrations used. The degree of micellization in the F68 system was lower than that in the P105 system, as revealed by the phase behaviour. A membrane-bound peptide, gramicidin D, and five different proteins were partitioned in the above systems. The proteins were lysozyme, bovine serum albumin, cytochrome c, bacteriorhodopsin and the engineered B domain of staphylococcal protein A, named Z. The Z domain was modified with tryptophan-rich peptide chains in the C-terminal end. It was found that effects of salt dominated over the temperature effect for the water-soluble proteins lysozyme, bovine serum albumin and cytochrome c. A strong temperature effect was observed in the partitioning of the integral membrane protein bacteriorhodopsin, where partitioning towards the more hydrophobic Pluronic phase was higher at 30 degrees C than at 5 degrees C. The membrane-bound peptide gramicidin D partitioned exclusively to the Pluronic phase at both temperatures. The following trends were observed in the partitioning of the Z protein. (i) At the higher temperature, insertion of tryptophan-rich peptides increased the partitioning to the Pluronic phase. (ii) At the lower temperature, lower values of K were observed for ZT2 than for ZT1.

Measurement of S-nitrosoalbumin by gas chromatography-mass spectrometry. I. Preparation, purification, isolation, characterization and metabolism of S-[15N]nitrosoalbumin in human blood in vitro

S-Nitrosoalbumin (SNALB) and S-[15N]nitrosoalbumin (S[15N]ALB) were prepared by various methods, purified and isolated by a novel selective extraction procedure using HiTrapBlue Sepharose affinity columns and characterized by various techniques including SDS-PAGE electrophoresis, UV-Vis spectroscopy and gas chromatography-mass spectrometry (GC-MS). S-Nitrosylation of albumin in freshly obtained human plasma by unlabeled and 15N-labeled butylnitrite at neutral pH revealed the purest preparations. For GC-MS analysis, SNALB and S[15N]ALB were treated with HgCl2 to obtain nitrite and [15N]nitrite, respectively, which were then analysed as their pentafluorobenzyl derivatives. S[15N]ALB preparations were standardized by GC-MS using nitrite as internal standard. S[15N]ALB was prepared and isolated at concentrations of 188+/-43 microM (mean +/- SD, n = 8) at a final yield of about 45%, an isotopic purity of 98%, and SDS-PAGE electrophoretic purity of 90%. 15N-Labeled SNALB was used to study its metabolism in human blood. The half-life of S[15N]ALB (25 microM) in human heparinized blood in vitro was determined by GC-MS as 5.5 h. The GC-MS method described here could be useful for the quantitative determination of SNALB in human plasma using S[15N]ALB as an internal standard.

Continuous foaming for protein recovery: part II. Selective recovery of proteins from binary mixtures

Foam separation may have potential for protein recovery. However, for foam separation to be a viable protein recovery technique it is important to demonstrate, not only that high enrichments and recoveries can be achieved for single proteins, but also that high enrichments and recoveries, together with selectivity of partition, can be achieved for recovery from multi-component mixtures. Most process streams which require purification are indeed complex multi-component mixtures, for example, fermentation broths. In this study, three binary protein mixtures were chosen for continuous foam separation: beta-casein:lysozyme; Bovine serum albumin (BSA):lysozyme and beta-casein:BSA (mixtures 1, 2, and 3, respectively). For each of these mixtures, the expected outcome of each experiment, based on a previous knowledge and determination of relevant protein physical properties, was that the first protein should be preferentially separated into the foam phase. On the basis of results reported in Part I of this study for the continuous foam separation of beta-casein, conditions found to favor maximum enrichment were selected. For each mixture a range of concentrations of both proteins was considered. For mixture 1, maximum protein recoveries in the foam phase were 85.6% and 25% for beta-casein and lysozyme, respectively; and for mixture 2, maximum recoveries of 77. 6% and 18.9% were obtained for BSA and lysozyme, respectively. Maximum enrichment ratios in the foam phase were 79.4 and 2.5 for beta-casein and lysozyme respectively in mixture 1; and 74.0 and 1.4 for BSA and lysozyme respectively in mixture 2. Selective partitioning of beta-casein and BSA into the foam phase was obtained in mixtures 1 and 2, respectively, particularly for protein concentrations at which dilute protein films are known to form at the gas-liquid interface in the foam. Maximum partition ratios for mixtures 1 and 2 were 31.8 and 52.8, respectively. For mixture 3, both BSA and beta-casein were enriched into the foam phase. Maximum enrichments were 42.9 and 24.7 for BSA and beta-casein, respectively; however, selective partitioning in mixture 3 was limited (maximum partition ratio being 1.8).

Investigations on protein adsorption to agarose-dextran composite media

A new stationary phase for protein purification was investigated with regard to its performance during capture of selected model proteins. The commercially available matrix consists of a porous agarose backbone, to which dextran is covalently attached. The dextran carries ion-exchange ligands, thus providing a binding space of high ligand density. Breakthrough of various proteins during frontal application to packed beds was measured and the experiments were analyzed in terms of equilibrium and breakthrough capacity. A significant increase of static capacity, as compared with conventional porous matrices, was found. Good dynamic properties allowed utilization of a high percentage of the equilibrium capacity at 10% breakthrough. For all proteins, a decreasing ratio of breakthrough to equilibrium capacity was detected with increasing feed concentration. This observation suggested a significant contribution of solid diffusion to the transport of proteins into the adsorbent particles. The specific architecture of the stationary phase, where the agarose base structure is derivatized with ion-exchange ligand-bearing dextran, may lead to this behavior.