Purification of chymotrypsin by subunit exchange chromatography on the denatured protein.
The alpha-chymotrypsin subunits immobilized under denaturing conditions (6 M urea or 1% SDS) on CNBr-activated Sepharose 4B, were found to interact with soluble chymotrypsin subunits with the formation of oligomers higher than dimers. Subunits immobilized under nondenaturing conditions form only dimers. The effects of several parameters, such as organic solvents, cations, and anions of the lyotropic series, on the associating properties of the immobilized derivatives were examined. The interaction between immobilized and free enzyme was shown to be specific because extraneous proteins and compounds were not bound by the derivatives. Chymotrypsinogen, studied analogously, did not show appreciable self-associating capacity. Chymotrypsin subunits immobilized under denaturing conditions and packed in a column proved to be suitable for the purification of chymotrypsin from both bovine and porcine pancreatic extracts. The "subunit exchange" chromatography of such extracts, carried out between pH 2.5 and 4, gave an eightfold purification with a 93% recovery of chymotryptic activity. The specific activity was ca. 12,000 Schwert and Takenaka units/mg. Only 6% of the tryptic activity was bound by the column. The capacity of the matrix, 6 mg chymotrypsin/mL, dropped to about 70% of the original value after.
Instituto di Chimica degli Ormoni, CNR, Via Mario Bianco 9, 20131 Milano, Italy.
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Carrea
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Pasta
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Antonini