2001 Volume 27 Issue 2 Pages 186-190
Molecular recognition in hydroxyapatite chromatography (HAG) and ion exchange chromatography (IEC) is investigated. A fast and simple method for obtaining important information on the number of binding sites from linear gradient elution experiments (salt concentration is increased linearly at a fixed mobile phase pH) is first described. Linear gradient elution experiments for HAC and IEC were carried out with β-lactoglobulin (Lg) and Ribonuclease A (RNaseA) as model proteins. The experimental data were analyzed on the basis of the above-mentioned method.
The peak salt concentration IR and the number of binding sites B in IEC decrease as the mobile phase pH approaches the isoelectric points pl (Lg=5.1-5.3, RNaseA=9.7) for both Lg and RNaseA. The IR and B values of Lg in HAC decrease as the mobile phase pH increases. Although the IR values of RNaseA in HAC decrease with an increase in the mobile phase pH, the B values are constant (B ca. 5) and did not depend on the mobile phase pH. Two genetic variant forms of Lg, β-lactoglobulin A and β-lactoglobulin B, are not separated on HAC and cation-exchange chromatography. The two proteins are separated only on anion-exchange chromatography. On the basis of these experimental findings the molecular recognition mechanism of HAC with Lg and RNaseA is discussed in comparison with the mechanism in IEC.
