Protein Separation with Ion-exchange Membrane Chromatography

Cao, Liming

Etd

Protein Separation with Ion-exchange Membrane Chromatography

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Membrane chromatography is a promising process for the isolation, purification, and recovery of proteins, enzymes, and nuclear acids. Comparing with traditional beads column chromatography, membrane chromatography can faster, easier and cheaper to mass-produce. And also, it is easy to set up and scale up. In this thesis, we are trying to study the performance of membrane chromatography, and the mixture of HSA and chicken egg white is used as an example. We are investigating the purification of Human serum albumin (HSA) from chicken egg white in terms of precondition, dilution, purification method, product recovery, product purity and product cost. HSA, is a very important clinical protein. In order to obtain low cost, high efficiency and less risk HSA, recombinant DNA technology is used. Many kinds of host organism have been used to produce recombinant HSA (rHSA). In this thesis, a kind of ion-exchange membrane (Mustang Q membrane capsule) chromatography was used. The membrane capsule is disposable because it is designed for use in pharmaceutical production. For this project, a cleaning method was used which made the membrane capsule reusable. Washing with 4 mL 1 M NaCl and 4 mL NaOH was sufficient for this purpose. Since the egg white protein solution was very viscous, it needs to be diluted before loaded on FPLC. Dilute experiment was done to find the best dilution level. In this thesis, we found that 5 times dilution was best not only for high efficiency but also for FPLC operation. After getting the basic conditions, some purification experiments were done to find the optimal operation condition to purify HSA form chicken egg white protein solution by changing buffer pH, salt concentration in elution buffer and gradient used to elute proteins. The best purification condition for loading buffer is Tris-HCl buffer A (4.75g/L, pH 9.5) and the elution buffer is Tris-HCl buffer A + 0.2M NaCl. The purity of HSA recovered was 93% on the Mustang Q membrane capsule at 1 ml/min when the mixture of HSA and chicken egg white was diluted 10 times. And the yield was 85%. The impurity is probably ovoglobulin as suggested by the result of SDS-PAGE, whose molecular weight is close to 40kd. To characterize the separation capability of the Mustang Q membrane capsules, equilibrium adsorption and breakthrough curve studies were made using bovine serum albumin (BSA). 1mg/mL BSA solution was used to get the breakthrough curve with different flow rate ranging from 1 to 4 ml/min. With a flow rate is 1 ml/min, breakthrough curve were obtained with different concentrations of BSA ranging from 1 to 16 mg/mL. The dynamic binding capacity was found to be from 9.1 to 119.1 mg/mL. The equilibrium adsorption isotherm showed Langmuir isotherm behavior with dissociation constant and a maximum adsorption capability. According to the result of isotherm adsorption, a multi-plate mathematical model was used to get the theoretical breakthrough curve. By fitting the theoretical breakthrough curve to the experimental breakthrough curve, constants in the multi-plate model were obtained and were used to estimate the axial dispersion coefficient of the membrane capsule. The estimated axial dispersion coefficient of 2.45*10-6 cm2/s is very small which means that the axial ispersion is not significant. The adsorption process is therefore controlled by radial radius dispersion or film dispersion.

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