High-performance liquid affinity chromatography with phenylboronic acid, benzamidine, tri-L-alanine, and concanavalin A immobilized on 3-isothiocyanatopropyltriethoxysilane-activated nonporous monodisperse silicas

High-gradient magnetic affinity separation of trypsin from porcine pancreatin

We introduce a robust and scale-flexible approach to macromolecule purification employing tailor-made magnetic adsorbents and high-gradient magnetic separation technology adapted from the mineral processing industries. Detailed procedures for the synthesis of large quantities of low-cost defined submicron-sized magnetic supports are presented. These support materials exhibit unique features, which facilitate their large-scale processing using high magnetic field gradients, namely sufficiently high magnetization, a relatively narrow particle size distribution and ideal superparamagnetism. Following systematic optimization with respect to activation chemistry, spacer length and ligand density, conditions for preparation of effective high capacity (Q(max) = 120 mg g(-1)) strongly interacting (Kd < 0.3 microm) trypsin-binding adsorbents based on immobilized benzamidine were established. In small-scale studies approximately 95% of the endogenous trypsin present in a crude porcine pancreatin feedstock was recovered with a purification factor of approximately 4.1 at the expense of only a 4% loss in alpha-amylase activity. Efficient recovery of trypsin from the same feedstock was demonstrated at a vastly increased scale using a high-gradient magnetic separation system to capture loaded benzamidine-linked adsorbents following batch adsorption. With the aid of a simple recycle loop over 80% of the initially adsorbed trypsin was recovered in-line with an overall purification factor of approximately 3.5.

Microcalorimetric studies on the interaction mechanism between proteins and hydrophobic solid surfaces in hydrophobic interaction chromatography: effects of salts, hydrophobicity of the sorbent, and structure of the protein

This study examines the effects of different salts as well as the influence of the relative hydrophobicities of different sorbents on the adsorption processes of proteins in hydrophobic interaction chromatography (HIC). Comparative data acquired by the equilibrium binding analysis and by isothermal titration microcalorimetry (ITC) are presented. In particular, thermodynamic parameters, including the enthalpy changes, related to the interactions between several globular proteins and various Toyopearl 650 M sorbents under solvent conditions containing either 2.0 M ammonium sulfate or 2.0 M sodium sulfate at pH 7.0 and 298.15 K have been evaluated in terms of the molecular properties of these systems. The results reveal that the dependence of the free energy change, deltaGads, for protein adsorption to HIC sorbents on the salt composition can be mainly attributed to the enthalpy changes associated with protein and sorbent dehydration and hydrophobic interactions. Differences in binding mechanisms between the n-butyl- and phenyl-HIC sorbents were evident. In the latter case, the participation of pi-pi hydrophobic interactions leads to significant differences in the associated enthalpy and entropy changes. Furthermore, an increase in the hydrophobicity of either the sorbent or the protein resulted in more negative values for the free energy change, which arose mostly from dehydration processes. Entropic effects favoring HIC adsorption increased with an increase in the exposed nonpolar surface area of the protein. Consequently, an increased contribution from the entropy change to the respective change in free energy occurs when HIC sorbents or proteins of higher hydrophobicity are employed, with these larger entropy changes consistent with a change in the interaction mechanism from a binding event dominated by adsorption to a partitioning-like process. Data extracted from the ITC measurements also provided insight into the interaction mechanisms that occur between proteins and hydrophobic solid surfaces, yielding information that can be applied to the HIC purification of proteins according to the concept of critical hydrophobicity of the system and its thermodynamic consequences.

Comparative studies on the isothermal characteristics of proteins adsorbed under batch equilibrium conditions to ion-exchange, immobilised metal ion affinity and dye affinity matrices with different ionic strength and temperature conditions

In these investigations, the influence of a range of experimental parameters on the isothermal characteristics of hen egg white lysozyme (HEWL) and human serum albumin (HSA) adsorbed to several different adsorbents has been examined. The adsorbents were selected to encompass the same basic types of silica support matrices, but with the ligand properties and surface characteristics adjusted so that the dominant mode of interaction between the protein and the ligand involved either electrostatic binding (i.e. as ion-exchange interaction with polyaspartic acid immobilised onto glycidoxypropyl-modified Fractosil 1000), mixed-mode binding with both hydrophobic and electrostatic effect contributing to the protein-ligand interaction (i.e. as dye-affinity interactions with Cibacron Blue F3G-A immobilised onto Lichroprep DIOL or onto glycidoxypropyl-modified Fractosil 1000), or lone pair coordination binding (i.e. as immobilised metal ion affinity (IMAC) interactions with Cu2+ ions complexed with iminodiacetic acid immobilised onto glycidoxypropyl-modified Fractosil 1000). In each case, the adsorbents exhibited similar ligand densities and had the same particle size ranges and silica surface pretreatment. The effect of the ionic strength of the adsorption buffer and temperature on the isothermal adsorption behaviour under batch equilibrium binding conditions of the two test proteins were determined. Consistent with previous observations with soft gel ion exchangers and triazine dye-based adsorbents that are used in packed bed chromatographic systems, the capacities of the silica-based ion-exchange adsorbents, as well as the Cibacron Blue F3G-A dye affinity adsorbents, for both HSA and HEWL were reduced as the salt concentration was increased under batch equilibrium binding conditions. Moreover, with both of these classes of adsorbents, as the ionic strength was increased under constant temperature conditions, the isothermal adsorption dependencies progressively approximated more closely a Langmuirean model of independent binding site interactions, typical of a mono-layer binding process. In contrast, with the silica-based immobilised metal ion affinity adsorbents as the ionic strength was increased the adsorption behaviour appeared to follow a Freundlich model, indicative of positive cooperativity in the binding process. In parallel experiments, the effect of changes in temperature under iso-ionic strength conditions was examined. With increasing temperature, different patterns of isothermal adsorption behaviour for both test proteins were observed, with the magnitude of these trends depending on the type of interaction involved between the immobilised ligand and the protein. Utilising first order Van't Hoff relationships to analyse the experimental data for these protein-ligand interactions, the apparent changes in enthalpy and entropy for these interactions have been derived from the dependency of the change in the apparent Gibbs free energy on 1/T.

Porous zirconia: a new support material for enzyme immobilization

Four different proteases (trypsin, chymotrypsin, papain and pepsin) were covalently attached to the surface of a new type of porous zirconia, as well as a conventional porous silica, activated with 3-isothiocyanatopropyltriethoxy silane (NCS-silane). The immobilization efficiency onto the porous zirconia material was evaluated in terms of the amount of enzyme attached to the particles and from the biological activity remaining after the immobilization step. The results were compared with the corresponding experiments with a porous silica of similar surface area/g support material. In addition, the storage stability of the modified zirconia and silica biocatalysts were evaluated. These results indicated that specific immobilized enzyme biocatalysts can be achieved with this new zirconia support material which exhibits different properties to those observed with the more conventional silica-based materials. Moreover, the results with the enzyme-zirconia biocatalysts also indicate different characteristics when compared with data for the same enzymes immobilized under similar buffer conditions to organic support materials as previously described by various other investigators. The advantages of zirconia-based immobilized enzyme biocatalysts in terms of their density and chemical robustness are also described relative to other alternative support materials currently in use.

High-performance liquid chromatography of amino acids, peptides and proteins. CXXX. Modified porous zirconia as sorbents in affinity chromatography

The utilisation of organosilanes to introduce active chemical groups onto zirconia surfaces, suitable for the subsequent immobilisation of proteins or other biomimetic ligands, is described. Two different types of porous zirconia-based particles with nominal pore diameters of 160 and 1000 A pore size were modified with two different affinity ligands. In the first case, methods to immobilise iminodiacetic acid-Cu(II) and its application in Cu(II) immobilised metal ion affinity chromatography (IMAC) were established. In the second series of experiments, concanavalin A was immobilised and the interaction of this lectin with the enzyme horseradish peroxidase examined. For both systems, adsorption isotherms were recorded as batch experiments. In each case, the experimental results could be fitted to langmuirean type adsorption isotherms, indicating that under the chosen conditions only one type of interaction is present, with nonspecific interactions with the support surface playing an insignificant role. These studies document the potential of surface modified zirconia particles for the immobilisation of chemical ligands or proteins for use in biospecific affinity chromatography and immobilised enzyme bioreactors.

High-performance affinity chromatography of NADP+ dehydrogenases from cell-free extracts using a nucleotide analogue as general ligand

An epoxy-activated silica column (50 cm x 0.45 cm I.D.) was derivatized with 8-[6-aminohexyl)amino]-2'-phosphoadenosine-5'-diphosphoribose; the bound ligand concentration was 11.4 mumol/g of dry silica, and the useful loading capacity was 2.3 mg of glutathione reductase. The new high-performance liquid chromatographic column specifically retained NADP(+)-dependent enzymes, which were quantitatively eluted specifically by NADP+ or, with better resolution, by potassium chloride. The new high-performance liquid chromatographic support was applied to the purification of glutathione reductase and glucose-6-phosphate dehydrogenase from cell-free extracts of baker's yeast, fish liver and rabbit hemolysates, with high recoveries and excellent purification factors.

High-performance liquid chromatography of amino acids, peptides and proteins. CIX. Investigations on the relation between the ligand density of cibacron blue immobilized porous and non-porous sorbents and protein-binding capacities and association constants

A porous silica of nominal 5 microns particle diameter and 30 nm pore size (Nucleosil 300-5) and a non-porous silica of nominal 1.5 microns particle diameter were activated with 3-mercaptopropyltriethoxysilane (MPTS), followed by the immobilization of the triazine dye, Cibacron Blue F3GA. Various biomimetic dye sorbents with graduated ligand densities between 1 mumol/m2 and 0.01 mumol/m2 were prepared. The capacities and the association constants associated with the binding of lysozyme to these sorbents were determined by frontal analysis experiments [J. Chromatogr., 476 (1989) 205-225]. Due to the ability of the Cibacron Blue F3GA-modified silicas to act as mixed mode coulombic and hydrophobic interaction sorbents and the highly charged nature of the surface structure of lysozyme (pl 11), two mobile phase conditions were examined. In one case a 0.1 M phosphate buffer, pH 7.8, was used as the equilibration and loading buffer, in the second case 1 M sodium chloride-0.1 M phosphate buffer, pH 7.8 was employed as the equilibration and loading buffer to monitor the influence of ionic interactions. The elution was performed in each case with a 2.5 M potassium thiocyanate solution. With the porous silica dye sorbents and 1 M NaCl present in the loading buffer, the highest capacity was achieved when Cibacron Blue F3GA was immobilised to the level of 0.1 mumol/m2. In the case of the non-porous silica dye sorbents, the maximum protein capacity was achieved when 0.5 mumol/m2 dye were immobilised onto the support. Evaluation of the frontal breakthrough curves confirmed that the kinetics of adsorption of lysozyme onto the non-porous sorbent were substantially faster than the adsorption of lysozyme onto the porous sorbent due to the absence of pore diffusion effects in case of the non-porous support. Furthermore, the adsorption of lysozyme on both sorbents was faster when no salt was added to the loading buffer, indicating that there is either conformational or reorientation effects operating during the specific binding of the protein to the dye ligand, or that the interaction is proceeding through the participation of a second class of binding sites. The magnitude of the association constants, Ka, for the lysozyme-Cibacron Blue F3GA systems were found to be dependent on the ligand density of the sorbent. With decreasing ligand density, the protein-ligand interaction became stronger, e.g. Ka values became larger. These results confirm earlier observations on the effect of ligand steric compression on the affinate-ligand association constant, e.g. the protein needs sufficient space to interact with the ligand in an optimum way.(ABSTRACT TRUNCATED AT 400 WORDS)

Immobilization of binding proteins on nonporous supports. Comparison of protein loading, activity, and stability

Four different nonporous particulate materials, nylon, polystyrene, soda-lime silicate glass, and fused silica glass, have been evaluated for their appropriateness as immobilization supports for immunoglobulins. A method of protein quantitation that is usually applied to solutions, the bicinchoninic acid (BCA) assay, was used successfully to directly measure ng amounts of protein immobilized on the supports. Two proteins, a monoclonal antibody to theophylline and the biotin binding protein avidin, were studied. Radioactive theophylline and radioactive biotin were used to measure the activity of the immobilized protein. Ligand binding capacity per mm2 of support was measured as a function of amount of protein immobilized. By measuring both the amount of protein immobilized and its ligand binding capacity, we have determined that antitheophylline antibody adsorbed on polystyrene balls loses almost 90% of its binding activity after 65 h, although little protein is lost from the balls over this time. Avidin retains nearly full activity for biotin on polystyrene. The binding activity of biotinyl-antibody conjugate immobilized on avidin-adsorbed polystyrene is stable, even when stored for over 22 wk. Antibody covalently immobilized on soda-lime silicate glass beads retains its binding activity over long-term storage, although only 0.1 mol of 3H-theophylline bind per mol of immobilized antibody. Using fused silica glass particles as the solid support, the same antibody binds approx 0.6 mol of ligand per mol of immobilized antibody protein. The structural "softness" of the immunoglobulin requires that interaction with the surface be prevented in order to maintain activity.

High-performance liquid chromatography of amino acids, peptides and proteins. XCV. Thermodynamic and kinetic investigations on rigid and soft affinity gels with varying particle and pore sizes: comparison of thermodynamic parameters and the adsorption behaviour of proteins evaluated from bath and frontal analysis experiments

The thermodynamic constants, associated with the interaction of three proteins with triazine dye affinity sorbents, have been derived from bath and frontal analysis experiments. In cases where mass-transfer restrictions are very high, calculation of the thermodynamic constants directly from frontal analysis experiments could not be achieved. In such cases, a portion of the adsorbate was always present in the effluent, a situation which has its effect as the split peak phenomenon. With Fractogel-based triazine dye affinity sorbents none of the test proteins applied in frontal analysis were adsorbed. A similar behaviour was observed for a Cellufine sorbent during the adsorption of human serum albumin and the Blue Sepharose CL6B sorbent during the adsorption of alcohol dehydrogenase, which displayed much slower apparent adsorption kinetics than observed in the bath experiments. These phenomena were shown to be associated with changes in the gel structure, caused in part by the column packing procedure. Silica-based sorbents performed better in the adsorption of lysozyme in the column mode than soft-gel affinity sorbents, as was evident in the higher capacities and steeper breakthrough curves. At high protein concentrations (feedstock concentration greater than 0.2 mg/ml) breakthrough curves obtained with small- and large-particle-size sorbents, but of constant pore size, were found to be identical. This finding demonstrates that the use of small-particle-size sorbents (e.g. particle diameter, dp less than or equal to 5 microns) for the preparative isolation of proteins may not be justified when operating in the overload mode. With other higher-molecular-weight proteins and the silica-based sorbent systems examined, the small-particle-size sorbents (dp = 5 microns) displayed less symmetrical shapes of their breakthrough curves than the larger-particle-size and soft-gel sorbents. This behaviour was further exacerbated when non-porous glass or silica-based sorbents were utilized. These non-porous affinity sorbents displayed nearly rectangular breakthrough shapes at the onset of the adsorption process, but comparatively slow adsorption kinetics became evident as saturation was approached. This phenomenon has been attributed to surface rearrangement and/or reorientation of the adsorbed proteins, particularly with sorbents of high ligand densities.