Lysozyme adsorption and purification by expanded bed chromatography of a customized Nd-Fe-B alloy-densified agarose (NFBA) gel modified with Cibacron Blue 3GA (CB) were investigated, and the results were compared with those obtained with CB-modified Streamline gel (CB-Streamline). The NFBA gel had a mean size of 102m and a mean density of 1.88g/ml. The breakthrough behavior of lysozyme was modeled considering the dispersion of the liquid and solid phases and the diffusive mass transport of protein to the solid phase. Using independently determined parameters, the model prediction agreed reasonably well to the experimental data. Although the two dye-ligand adsorbents showed nearly the same static capacity, the dynamic binding capacity of the CB-NFBA gel was nearly twice that of the CB-Streamline gel. Moreover, lysozyme was purified from chicken egg white solution by the expanded beds with the two adsorbents, and the expanded bed with the CB-NFBA gel produced much larger purification factor than that with the CB-Streamline gel.All the results indicated that the small-sized dense medium CB-NFBA gel was more efficient as an expanded bed adsorbent.

Protein renaturation is of importance in the recovery of inclusion-body protein produced by recombinant microbial cells. It has been recognized that the artificial chaperone system, Cetyltrimethylammonium bromide and β-cyclodextrin, are effective in enhancing protein renaturation. Using chicken egg white lysozyme as a model protein, this work studied protein renaturation by size exclusion chromatography (SEC) incorporating with the artificial chaperone system. At first, a cooperative effect of the artificial chaperones and guanidinium chloride (GdmCl) on the protein renaturation was confirmed, and it was concluded that the artificial chaperone system promoted the renaturation of lysozyme (1.05mg/ml) in the presence of 1mol/liter GdmCl. Using the SEC (29.5×2.6cm I.D., packed with Sephacryl S-100h gel) incorporating with the artificial chaperones, higher renaturation yield was obtained at high flow rate (0.8-2.2ml/min). In contrast, using the SEC without the artificial chaperones, very low flow rate (i.e.<0.4ml/min) should be used to receive a comparable renaturation yield. Thus, use of the SEC incorporating with the artificial chaperone system would greatly benefit in reaching a high refolding productivity.

The nonionic surfactant of sorbitan trioleate (Span 85) was modified with Cibacron Blue F-3GA (CB) as an affinity surfactant (CB-Span 85) to form affinity-based reversed micelles in n-hexane. The reversed micelles formed by the mixture of Span 85 and CB-Span 85 conjugate were extensively characterized in water content, hydrodynamic radius, and aggregation number. The results show that the water content and hydrodynamic radius of the reversed micelles were significantly increased by the introduction of CB ligands (CB-Span 85 conjugate), and the reversed micelles with CB-Span 85 conjugate had a wider aggregation number distribution than the Span 85 reversed micelles. Using lysozyme as a model protein, protein solubilization by the reversed micelles was investigated. Lysozyme solubilization increased significantly with the coupled CB concentration, indicating that the extraction was based upon the affinity interactions between lysozyme molecules and the CB ligand. High solubilization of lysozyme was obtained by the affinity-based reversed micelles of 62.7mmol/L Span 85 with coupled CB higher than 0.25mmol/L. Lysozyme recovery was carried out using a stripping solution of high ionic strength. The recovered lysozyme exhibited an activity equivalent to the native lysozyme and its secondary structure was also unchanged. The results indicate that the reversed micellar system would find potential application in protein separation.

A refolding chromatography with immobilized molecular chaperonin GroEL was studied for the reactivation of denatured-reduced lysozyme. The effect of denaturant concentration (guanidine hydrochloride, 0.1-1.5M) in the elution buffer, the elution flow-rate, and the loading concentration and volume of the substrate protein on the reactivation yield was studied. All the operating parameters showed minor effects on the recovery yield of lysozyme mass, which remained at 90-100%, but exhibited relatively notable influences on the specific activity of the recovered lysozyme. For example, thereexisted an optimum denaturant concentration of about 1 M at which the highest yield of specific activity (up to 97%) was obtained. Using the immobilized GroEL column, 3ml of the lysozyme (1mg/ml) per batch could be refolded at an overall yield of 81%, which corresponded to a refolding productivity of 54mg per l gel per h. At comparable reactivation yields (over 80%), this value of productivity was over four-times larger as that of the size-exclusion refolding chromatography reported previously (12mg per 1gel perh), indicating the advantage of the present system for producing a high throughput in protein refolding operations.

A heptapeptide phage display library was screened with insulin to find its ligands for affinity chromatography. The peptide was synthesized and coupled to EAH Sepharose 4B (5.4umol mL-1 bed). Then, insulin chromatography was carried out with mobile phases of different pH values and by the addition of urea and ethylene glycol. It was found that electrostatic interactions were predominant for the affinity binding, and hydrogen bonding might also contribute somewhat to the affinity. Finally, frontal analysis was performed and the dynamic binding capacity of the affinity column for insulin at 50% breakthrough was estimated at 60.6mg mL-1 bed, which was about two times higher than the theoretical binding capacity of the monomeric insulin. The result suggests that insulin was bound in dimer state in a stoichiometric relationship with the coupled peptide, indicating the high binding efficiency of the peptide ligand for insulin.