High-performance liquid chromatography of amino acids, peptides and proteins

A novel two-zone protein uptake model for affinity chromatography and its application to the description of elution band profiles of proteins fused to a family 9 cellulose binding module affinity tag

A novel two-zone model (TZM) is presented to describe the rate of solute uptake by the stationary phase of a sorption-type chromatography column. The TZM divides the porous stationary-phase particle into an inner protein-free core and an outer protein-containing zone where intraparticle transport is limited by pore diffusion and binding follows Langmuir theory. The TZM and the classic pore-diffusion model (PDM) of chromatography are applied to the prediction of stationary-phase uptake and elution bands within a cellulose-based affinity chromatography column designed to selectively purify proteins genetically labelled with a CBM9 (family 9 cellulose binding module) affinity tag. Under both linear and nonlinear loading conditions, the TZM closely matches rates of protein uptake within the stationary phase particles as measured by confocal laser scanning microscopy, while the PDM deviates from experiment in the linear-binding region. As a result, the TZM is shown to provide improved predictions of product breakthrough, including elution behavior from a bacterial lysate feed.

New insights in the spatially resolved dynamic pH measurement in macroscopic large absorbent particles by confocal laser scanning microscopy

Both, experimental investigation of protein adsorption processes and mathematical models describing such processes indicate, that the pH in the absorbent particle might be the key factor for an improved understanding of these chromatographic processes. Thus, a technique aiming at the spatially resolved pH measurement in macroscopic large absorbent particles is presented. The first application of this method, being based on confocal laser scanning microscopy (CLSM), revealed an apparent dependence of the pH calibration curve on the scanning depth. By a model-based approach, factors distorting the measurement signal are identified: The wavelength-dependent light scattering and the re-absorption of emitted light. The resulting consequences for further development and application of CLSM based techniques to measure pH in macroscopic large absorbent particles are illustrated and discussed.

Mechanism and kinetics of protein transport in chromatographic media studied by confocal laser scanning microscopy

The impact of different transport mechanism on chromatographic performance was studied by confocal laser scanning microscopy (CLSM) for solutions containing bovine serum albumin (BSA) and monoclonal IgG 2a under different solid- and fluid-phase conditions. During this investigation, a clear influence of the uptake mechanism on the affinity of the respective proteins for the different adsorbents and thus separation performance of the chromatographic process could be observed. For the system SP Sepharose Fast Flow at pH 4.5 pore diffusion could be ascribed to be the dominant transport mechanism for both proteins and the adsorption profiles resembled a pattern similar to that described by the 'shrinking core' model. Under these conditions a significantly higher affinity towards the adsorbent was found for BSA when compared to IgG 2a. With changing fluid- and solid-phase conditions, however, a change of the transport mode for IgG 2a could be detected. While the exact mechanism is still unresolved it could be concluded that both occurrence and magnitude of the now governing transport mechanism depended on protein properties and interaction with the adsorbent surface. For the system SP Sepharose XL at pH 5.0 both parameters leading to the change in IgG 2a uptake were combined resulting in a clear change of the system affinity towards the IgG 2a molecule, while BSA adsorption was restricted to the most outer shell of the sorbent.

Mechanism and kinetics of protein transport in chromatographic media studied by confocal laser scanning microscopy

An experimental study on the interplay of sorbent structure and fluid phase conditions (pH) has been carried out examining adsorption and transport of bovine serum albumin (BSA) and a monoclonal antibody (IgG 2a) on SP Sepharose Fast Flow and SP Sepharose XL. SP Sepharose Fast Flow is characterised by a relatively open pore network, while SP Sepharose XL is a composite structure with ligand-carrying dextran chains filling the pore space. Both adsorbents have similar ionic capacity. Protein transport and adsorption profiles were evaluated using confocal laser scanning microscopy. Under all investigated conditions, BSA uptake could be adequately explained by a pore diffusion mechanism. The adsorption profiles obtained for IgG 2a, however, indicated that changes in fluid phase conditions as well as a change in the solid phase structure could result in a more complex uptake mechanism as compared to pore diffusion alone. This mechanism results in a fast transport of proteins into the adsorbent, followed by an overshoot of protein in the center of the sorbent and a setback towards a homogeneous adsorption profile.

Protein adsorption on novel acrylamido-based polymeric ion-exchangers. IV. Effects of protein size on adsorption capacity and rate

The effects of protein size on the adsorption capacity and rate is determined for an acrylamido-based polymeric anion-exchanger. The proteins lactalbumin, myoglobin, ovalbumin, BSA, conalbumin, IgG, and ferritin with molecular masses ranging from 15,000 to 450,000 were investigated. At high salt concentration (50 mM Tris-HCl containing 500 mM NaCl), only the smaller proteins lactalbumin and myoglobin gained access to a significant portion of the particle volume. The larger proteins were nearly completely excluded, in agreement with the results obtained for neutral macromolecules. By contrast, at low salt concentration (50 mM Tris-HCl), the adsorption capacity was very large (280-400 mg/ml of particle volume) for all the proteins studied except for ferritin, for which the capacity was much lower. This suggests that, provided the solute is not too large, the favorable electrostatic interaction overcomes the size exclusion effect. Adsorption rate measurements showed that mass transfer rates are also quite fast at low salt concentration. Effective diffusivities were determined by matching model and experimental results and were found to decrease substantially as the protein size increased. As previously observed, the homogeneous diffusion model was found to predict the experimentally observed trends with respect to protein concentration and boundary layer mass transfer effects.

Comparison of protein adsorption isotherms and uptake rates in preparative cation-exchange materials

Adsorption isotherms and effective diffusivities of lysozyme in a set of six preparative cation-exchange stationary phases were determined from batch uptake data in a stirred vessel. Both a pore diffusion and a homogeneous diffusion model were used in estimating diffusivities, with the isotherms fitted to a non-Langmuirian analytical isotherm equation. The capacities inferred from the isotherms are found to be correlated with the surface area accessible to lysozyme, the effective surface concentrations obtained being in agreement with values measured by different methods in various non-chromatographic systems. The pore diffusivities show systematic trends with protein and salt concentration, and effects of pore size and connectivity are also evident. Some trends in the homogeneous diffusivities are quite different to those in the pore diffusivities, but these differences largely disappear when the homogeneous diffusivities are rescaled to account for adsorption equilibrium behavior. Additional information is required to elucidate further the mechanisms of coupled diffusion and adsorption in stationary phases.

High-performance liquid chromatography of amino acids, peptides and proteins. CXXXVIII. Adsorption of horse heart cytochrome c onto a tentacle-type cation exchanger

Determination of the change in the Gibb's free energy from the adsorption isotherm associated with the interaction between a biomolecule and an ion-exchange resin is often achieved by assuming that a Langmuirean model prevails. However, the adsorption of horse heart cytochrome c onto the tentacle-type cation exchanger LiChrospher 1000 SO3- at pH 4.00 showed an isotherm of rectangular form. In this case the Langmuirean model is not applicable. In this paper, we propose an alternative way to deal with this situation, whereby the adsorption capacity of the adsorbent with a defined protein sample is studied as a function of displacing-ion concentration. The experimental conditions over defined ranges are then selected in order to relate this function to the change in the Gibb's free energy for the interaction between the protein and the ion exchanger. Additional comments about the general utility of the on-line adsorption vessel system employed to determine the adsorption isotherms are also made.

High-performance liquid chromatography of amino acids, peptides and proteins. CXXVI. Modelling of protein adsorption with non-porous and porous particles in a finite bath

Analytical solutions for a mathematical model describing dynamic adsorption processes of proteins onto non-porous adsorbent particles in a finite bath are presented. The model, based on the Langmuir adsorption isotherm, has been applied to experimental data obtained with affinity and ion-exchange adsorbents. The external film mass transfer resistance, as well as the rate of surface interaction between proteins and adsorbents, have been taken into account. The model has been extended to the case of adsorption onto porous particles by employing a linear driving force approximation for describing mass transfer in the pore fluid. This approach enables the derivation of an effective overall liquid phase mass transfer coefficient, permitting subsequent adaptation of the analytical solutions developed for non-porous particles. The evaluation of the effective liquid phase mass transfer coefficients is also described. Examples of a comparison between predicted and experimental dynamic adsorption curves for both dye-affinity and ion-exchange systems are presented. The application of the model for predicting the optimum operating conditions is discussed.

High-performance liquid chromatography of amino acids, peptides and proteins. CXV. Thermodynamic behaviour of peptides in reversed-phase chromatography

The thermodynamic behaviour of three peptides, bombesin, beta-endorphin and glucagon, was studied under reversed-phase high-performance liquid chromatographic conditions. Experimental data related to the interactive surface contact area (S values) and solute affinity (log k0) were derived over a range of temperatures between 5 and 85 degrees C. These experimental conditions allowed changes in the secondary structure of the solute to be monitored. The influence of the nature of the stationary phase ligand on the relative conformational stability of the three peptides was analysed by acquiring data with n-octadecyl silica (C18) and n-butyl silica (C4) sorbents. Values for the relative changes in entropy and enthalpy associated with the interactive process were also determined. The results provide further insight into the factors involved with the stabilization of secondary structure and the mechanism of the interaction of peptides with hydrophobic surfaces.