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Physicochemical Properties and Amino Acid Composition of Chymotrypsinogen B

From the ¹ From the Department of Biochemistry, University of Alberta Medical School, Edmonton, Alberta, Canada

The physicochemical properties and amino acid composition of chymotrypsinogen B have been examined. The partial specific volume has been determined as 0.733 ml per g. From sedimentation velocity measurements, s_20,w⁰ has been found to be 2.58 S at pH 3.0. At pH values above 4, the zymogen dimerizes as indicated by both sedimentation velocity and approach to sedimentation equilibrium measurements. From light scattering and approach to sedimentation equilibrium measurements, an average molecular weight of 24,850 was calculated. Amino acid analyses performed in this laboratory are consistent with this value. The weight intrinsic viscosities of chymotrypsinogens A and B were found to be 2.18 and 2.26 ml per g, respectively. Comparison of the effective hydrodynamic volume calculated from the weight intrinsic viscosity and the viscosity increment with the value calculated from the partial specific volume of the anhydrous protein indicates that the molecule is relatively compact and sparingly hydrated in solution. Optical rotatory dispersion measurements of chymotrypsinogens A and B show that both zymogens have similar low helical contents and similar tertiary structures. An anomalous Cotton minimum at 221 mµ in chymotrypsinogen A is absent in chymotrypsinogen B and must represent some structural differences between the two proteins.

Amino acid analyses have shown significant differences in the levels of several of the amino acids, including lysine, arginine, aspartic acid, threonine, serine, glutamic acid, proline, methionine, and tyrosine. The half-cystine content has been determined as 10 and is consistent with the isolation of five unique disulfide sequences from this protein (3).

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