MOLECULAR WEIGHTS OF CHYMOTRYPSINOGEN AND CHYMOTRYPSIN α AND B

Abstract

From the studies of Kunitz and Northrop (1, 2) and of Jacobsen (3) it is known that chymotrypsin can exist in a number of active forms which have been designated as cq /3, and y (2) and, in addition, 6 and ?r (3).Laskowski and his collaborators (4-7) isolated a second form of the inactive zymogen, chymotrypsinogen B, and still another active enzyme which was named chymotrypsin B. The earlier form of chymotrypsinogen was called OL in conformity with the designation of its active form, chymotrypsin Q.The (Y and B series of proteins are distinguished by differences in method of preparation, solubility, electrophoretic mobility, and isoelectric point (4-7).The active enzymes, chymotrypsins a! and B, possess a similar action on synthetic substrates ( 8), but the B enzyme has a somewhat slower action on casein (6).The present investigation of sedimentation behavior in the ultracentrifuge and of diffusion was undertaken in order to characterize further chymotrypsin B and its zymogen and to compare them with the cr proteins under similar conditions.It was found that chymotrypsinogens c11 and B yield similar sedimentation and diffusion constants and, therefore, have the same molecular weight.We have confirmed the finding of Schwert (9) that solutions of chymotrypsin a! contain a mixture of monomeric and dimeric forms.Although chymotrypsin B shows a similar behavior at some pH values, it does exhibit monomeric behavior at pH 4. This has permitted a determination of the sedimentation and diffusion constants of this protein.It has been concluded from our data that the four proteins, the two zymogens and the two active enzymes, have the same size and shape in the monomeric form.EXPERIMENTAL