Rapid zymogen activation and isolation of serine proteases from an individual mouse pancreas by affinity chromatography: genetical heterogeneity of chymotrypsins of Mus musculus

A fluorescence stopped-flow kinetic study of the conformational activation of alpha-chymotrypsin and several mutants

The kinetic activation parameters (activation free energy, activation free enthalpy, and activation free entropy change) of the conformational change of alpha-chymotrypsin from an inactive to the active conformation were determined after a pH jump from pH 11.0 to pH 6.8 by the fluorescence stopped-flow method. The conformational change was followed by measuring changes in the protein fluorescence. For the bovine wild-type protein, the same kinetic parameters are obtained as in the study of proflavin binding. Several mutants were made with the goal to accelerate or decelerate this conformational transition. The inspiration for the choice of the mutants came from a previous modelling study done on the bovine wild-type chymotrypsin. The results of the fluorescence stopped flow experiments show that several mutants behaved as was expected based on the information provided by the modeling study on the wild-type variant. For some mutants our assumptions were not correct, and therefore additional modeling studies of the activation pathways of these mutant proteins are necessary to be able to explain the observed kinetic behavior.

Physico-chemical boundaries in the continuous and one-step discontinuous affinity-chromatographic isolation of proteins

From a physico-chemical point of view, affinity chromatography has no unambiguous definition. It is generally understood as the one-step chromatographic isolation of a protein from a biological sample. For such processes the protein recovery and the adsorption capacity for a given adsorption time is limited by static and dynamic physico-chemical properties of the system. The protein recovery is limited by the ratio of the static capacity, n(s), and the dissociation constant, K, for the interaction with the immobilized binding site. The limits of these quantities for 90% and 99% protein recovery were estimated. The residence time required to reach 90% of the adsorptive capacity of an adsorbent is a function of the above static properties, the pore-diffusion coefficient, D(p), and the diffusion distance in the adsorbent. It was estimated and was found to correlate well with experimental data. The one-step discontinuous or continuous chromatographic isolation of one protein from a biological sample by means of adsorbents that separate with respect to different properties is reviewed. This is only possible with selective specific adsorbents and, in special cases, also with bifunctional adsorbents that use hydrophobic interactions for the adsorption, and electrostatic repulsion for the desorption.

Expression of chymotrypsin(ogen) in the thioredoxin reductase deficient mutant strain of Escherichia coli AD494(DE3) and purification via a fusion product with a hexahistidine-tail

A reliable protocol was designed for fast expression and purification of recombinant chymotrypsin(ogen). The zymogen was overexpressed in soluble form as a (His)6-fusion construct in the cytoplasm of the thioredoxin reductase deficient Escherichia coli strain AD494(DE3). This allowed purification of chymotrypsinogen in a highly selective affinity chromatography capture step using a Ni-NTA column. After activation with enterokinase, the enzymatically active chymotrypsin was purified in a polishing step using a modified soybean trypsin inhibitor agarose column. This expression system and the use of affinity chromatography for capture and polishing, offers an easier and faster route to recombinant chymotrypsin(ogen) than the previously described use of Saccharomyces cerevisiae.

On the detection of functional and structural enzyme mutants by coordinated affinity chromatography and isoelectric focusing

A method of studying structural and functional heterogeneity of enzymes has been developed and tested on chymotrypsin. The enzyme, prepared from single mouse pancreata, has been fractionated with respect to function and charge content by a combination of affinity chromatography and isoelectric focusing. By comparing chymotrypsin isolated from isogenic strains, chymotrypsinogen of strains A/Sn and NZB was found to be genetically heterogeneous, thus not revealed as different chymotrypsin forms of a single zymogen. Chymotrypsinogen originating from two loci was investigated, and structural and functional differences of the corresponding enzymes were determined. At both loci, structural allelomorphism was indicated. At one locus, the structural heterogeneity was also found to be reflected in functional heterogeneity of the corresponding enzymes. By mating the two strains and fractionating the enzyme of the cross, the differences were shown to be inherited.