One step purification of chymosin by mixed mode chromatography.

Mixed mode Sepharose and Perloza bead cellulose matrices were prepared using various chemistries. These matrices contained hydrophobic (aliphatic and/or aromatic) and ionic (carboxylate or alkylamine) groups. Hydrophobic amine ligands were attached to epichlorohydrin activated Sepharose (mixed mode amine matrices). Hexylamine, aminophenylpropanediol and phenylethylamine were the preferred ligands, on the basis of cost and performance. Other mixed mode matrices were produced by incomplete attachment (0-80%) of the same amine ligands to carboxylate matrices. The best results were obtained using unmodified or partially ligand-modified aminocaproic acid Sepharose and Perloza. High ligand densities were used, resulting in high capacity. Furthermore, chymosin was adsorbed at high and low ionic strengths, which reduced sample preparation requirements. Chymosin, essentially homogeneous by electrophoresis, was recovered by a small pH change. The methods described were simple, efficient, inexpensive and provided very good resolution of chymosin from a crude recombinant source. The carboxylate matrices had the best combination of capacity and regeneration properties. The performance of Sepharose and Perloza carboxylate matrices was similar, but higher capacities were found for the latter. Because it is cheaper and can be used at higher flow rates, Perloza should be better suited to large scale application. High capacity chymosin adsorption was found with carboxymethyl ion exchange matrices, but low ionic strength was essential for adsorption and the purity was inferior to that of the mixed mode matrices.