pH dependence of ion‐exchange equilibrium of proteins

Analysis of steric mass-action model for protein adsorption equilibrium onto porous anion-exchange adsorbent

“…The values of K a , and a for -chymotrypsinogen were 7.58/3.17, 0.46/0.39 and 8500/1500 (BioScale/UNO), respectively. The adsorption equilibrium of BSA onto a strong anion exchanger, Q-Sepharose FF, with an ion-exchange capacity of 200 mmol/l was investigated by Bosma and Wesselingh (1998). In their study, the values of and a of BSA in pH 7.8 Tris-HCl buffer were 4.3 and 142, respectively.…”

“…At lower pH close to the isoelectric point of BSA (pI 4.9) (Johnson et al, 1995), the precision of the model prediction further decreased. It is well known that the protein is ampholyte, and the net charge and three-dimensional structure of protein are obviously influenced by pH of buffer solutions (Tanford et al, 1955;Neal et al, 1984, Bosma andWesselingh (1998)). Tanford et al (1955) have proven that BSA exists in a compact form with increasing solution acidity in the pH range from 4.3 to 10.5.…”

“…At present, it is too difficult to establish a sophisticated model incorporating both the factors influencing the protein structure and the effect of salt concentration (Brooks and Cramer, 1992;Bosma and Wesselingh, 1998;Ståhlberg, 1999). (2) The neutral buffers are adopted in most chromatographic operations.…”

“…The model parameters and suitabilities are obviously influenced by the pH of the buffer solutions due to the net charge of protein as a function of pH (Bosma and Wesselingh, 1998;Bautista et al, 1999). A better understanding of the effect of pH of buffer solutions and ionic strength on model applicability would thus improve the modeling of the ion-exchange equilibrium.…”

“…In those studies, the most frequently used ones are the Langmuir model and its various modified forms (Fritz and Schlunder, 1974;Hu et al, 1992). The Langmuir model can be used to describe adsorption isotherms at constant pH and ionic strength (Whitley et al, 1989;Skidmore et al, 1990, Bosma andWesselingh, 1998). To describe the influence of salt concentration on the equilibrium, the double-layer model (Ståhlberg et al, 1992;Roth and Lenhoff, 1993;Ståhlberg, 1999), the competitive Langmuir-Freundlich isotherm (James and Do, 1991) and the Langmuir model with an empirical relation between the equilibrium constant and the salt concentration (Hu et al, 1992) were developed.…”