Non-specific binding in the affinity chromatography of chymotrypsin

Affinity chromatography for the purification of therapeutic proteins from transgenic maize using immobilized histamine

Plant molecular pharming is a technology that uses plants as bioreactors to produce recombinant molecules of medical and veterinary importance. In the present study, we evaluated the ability of histamine (HIM), tryptamine (TRM), phenylamine (PHEM) and tyramine (TYRM) coupled to Sepharose CL-4B via a 1,4-butanediol diglycidyl ether spacer to bind and purify human monoclonal anti-HIV antibody 2F5 (mAb 2F5) from spiked maize seed and tobacco leaf extracts. Detailed studies were carried out to determine the factors that affect the chromatographic behaviour of mAb 2F5 and also maize seed and tobacco leaf proteins. All affinity adsorbents showed a reduced capacity to bind and a reduced ability to purify proteins from tobacco extract compared to maize extract. Under optimal conditions, HIM exhibited high selectivity for mAb 2F5 and allowed a high degree of purification (>95% purity) and recovery (>90%) in a single step with salt elution (0.4 M KCl) from spiked maize seed extract. Analysis of the purified antibody fraction by ELISA and Western blot showed that the antibody was fully active and free of degraded variants or modified forms. The efficacy of the system was assessed further using a second therapeutic antibody (human monoclonal anti-HIV antibody mAb 2G12) and a therapeutic enzyme (alpha-chymotrypsin). HIM may find application in the purification of a wide range of biopharmaceuticals from transgenic plants.

The role of amino-terminal alanine in the control of conformation and activity of alpha-chymotrypsin

Novel acetylated derivatives of three different three-chained chymotrypsins were prepared from bovine chymotrypsinogen A and their catalytic properties and kinetics of denaturation in urea were compared with those of the corresponding non-acetylated enzymes. Measurements of the Km (apparent) as a function of pH confirmed earlier findings of Valenzuela and Bender [J. Biol. Chem. 248, 4909-4914 (1973)] that the alpha-species of chymotrypsin is much more sensitive to reversible inactivation at high pH compared to its sister three-chained chymotrypsins, alpha 1 and kappa-chymotrypsin. Similarly, the denaturation rate constants in 8 M urea of alpha-chymotrypsin were much more sensitive to high pH than alpha 1 and kappa-chymotrypsin. The urea denaturation study showed a transition at about pH 8 to a more urea-sensitive form of alpha-chymotrypsin, whereas alpha 1 and kappa-chymotrypsin were relatively insensitive to a change in pH from 6.5 to 10. When the N-terminal Ala149 of alpha-chymotrypsin was acetylated, thus preventing protonation of the N terminus, the active enzyme derivative displayed the same Km (app) vs pH profile as alpha 1 and kappa-chymotrypsin. Urea denaturation studies with this masked derivative also showed that the pH-dependent transition of native alpha-chymotrypsin at pH 8 was eliminated. These results demonstrate that it is the presence of the protonated Ala149 residue in alpha-chymotrypsin that accounts for much of the hypersensitivity of this enzyme species to inactivation and urea denaturation in the pH region 7.5-10.

Affinity chromatography of cells and cell membranes

This article attempts to introduce the concept of cellular affinity chromatography as it departs from molecular affinity chromatography. Special emphasis is placed on the selectio of a solid support as well as on the role of lectins as affinity ligands. Our major goal was to bring to light the basic principles involved, multiple options of ligands and matrices, and different techniques, which may be applied to separate the complex cell population as well as cell membranes. It is hoped that further developments in the field, especially in the selection of proper experimental conditions, ligands and matrix material may provide better results. We have tried to identify some of the potential problems which should be considered before these approaches can be used on a routine basis. Although the review deals primarily with the affinity chromatography of cells and cell membranes, examples are presented for diverse systems such as cell organelles, viruses and phages. A table summarizing the use of cellular affinity chromatography is included. It lists more than 80 examples covering the literature up to December, 1979.