Use of free-flow electrophoresis for the purification of components separated by ion-pair chromatography

Continuous free-flow electrophoresis

This review evaluates the literature on continuous free flow electrophoresis, published during the last four years. Its aim is to serve not only experts in the field but also newcomers, and, therefore, it also briefly describes the principles of the method and the techniques used, referring to fundamental papers published earlier. The actual commercial instrumentation is briefly outlined. A substantial part of this review is devoted to the optimization of the performance of this method. Finally, diverse applications of fractionations of charged species in solution, ranging from small ions to biological particles and cells, are surveyed.

Unstable proteins: how to subject them to chromatographic separations for purification procedures

The chromatographic separation of an unstable protein is often a challenge to the scientist working in the field of life sciences. Especially for the purification of sensitive enzymes, making use of conventional chromatographic techniques is difficult and frequently results in a complete loss of biological activity of the target protein. This report summarizes some general strategies that may help to keep unstable proteins in their native conformation during the rather harsh conditions of a purification procedure. In this context, a recently developed hollow fiber membrane module, suitable for performing on-line dialysis, is introduced and examples of its application to liquid column chromatography are given. Many innovative separation techniques, characterized by dramatic improvements in both performance and separation time, have recently been developed. Since the chromatographic separation of unstable proteins requires the use of modern state-of-the-art equipment and technology, emphasis is given to newly developed separation techniques such as expanded bed adsorption, perfusion chromatography, protein free flow electrophoresis and the use of tentacle gels. In addition, examples of recently published purifications of unstable proteins are discussed with respect to strategies ensuring the preservation of the native protein structure during chromatographic separation.

Preparative isoelectric focusing in multicompartment electrolyzers: novel, hydrolytically stable and hydrophilic isoelectric membranes

Preparative isoelectric focusing in multicompartment electrolyzers is based on the production of isoelectric membranes of precise isoelectric point, able to buffer at their pI value and to titrate proteins tangent to or crossing the membranes. Up to the present, such membranes have been based on polyacrylamide chemistry; acrylamide, however, is neither stable in acidic nor basic environments. We describe here novel membranes, produced with a unique monomer, N-acryloylaminoethoxyethanol (AAEE). Poly(AAEE) membranes are extremely stable to alkaline hydrolysis (500 times more stable than polyacrylamide) and even more hydrophilic than the latter matrix. This allows production of highly reproducible membranes (these do not change their pI with time, since no acrylic acid is produced by hydrolysis upon storage) which do not adsorb proteins by hydrophobic interaction.

Free-flow electrophoresis for the purification of proteins: II. Isoelectric focusing and field step electrophoresis

Two modes of continuous isoelectric focusing are described. The development of a natural pH gradient, consisting of a mixture of three buffer solutions, and the focusing behavior of human serum albumin is investigated. The advantages of isoelectric focusing in an artificial pH gradient of three buffer solutions are demonstrated on the purification of alpha-amylase from an E. coli protein extract. Furthermore the principle of field step electrophoresis is presented. The most important factors influencing the efficiency: (i) residence time, (ii) conductivity of the sample and (iii) sample zone width, are discussed. The use of a larger sized device to allow simultaneous multiple injections of the sample demonstrates the feasibility of scaling-up field step electrophoresis. This approach permits a throughput of about 20 mL sample solution per minute.

Scale-up of free-flow electrophoresis: II. Purification of alcohol dehydrogenase from a crude yeast extract by field step electrophoresis and combined field step-zone electrophoresis

Results of the purification of alcohol dehydrogenase (ADH) by field step electrophoresis and combined field step-zone electrophoresis are presented. In field step electrophoresis, optimization of voltage, residence time and pH of the sample solution led to a maximal purification factor of 2.8 and a yield of 89% ADH. The limit of loading capacity was reached at a protein concentration of the sample solution of approximately 4 g/L, allowing a maximal throughput of 1.14 g/h with a yield of 86% and a 2.8-fold purification in the Elphor VaP 22 apparatus. With a production scale apparatus a throughput of 2.07 g/h without any loss of separation quality could be achieved. By introducing the sample solution into the separation chamber through 3 inlets, simultaneously, the throughput was increased to 3.2 g/h with a purification factor of 2.7 and a yield of 82% ADH. For the combined field step-zone electrophoresis method a maximum purification factor of 3.6 and a yield of 80% ADH were achieved. The loading capacity was limited to a 4.13 g/L protein concentration of the sample solution, resulting in a throughput of 440 mg/h. Injecting the sample solution simultaneously into 3 inlets resulted in a maximum throughput of 1.92 g/h with 3.1-fold purification and a yield of 80% ADH. Zone electrophoresis, field step electrophoresis and a combination of both are compared with respect to resolution, throughput and the application potential in a protein purification scheme. A scale-up to 3 g/h is possible in zone electrophoresis and field step electrophoresis.(ABSTRACT TRUNCATED AT 250 WORDS)