STUDIES OF CHYMOTRYPSINOGEN FAMILY OF PROTEINS .6. CHARACTERIZATION OF CONFORMATIONAL VARIATION OF CHYMOTRYPSIN

The structural variation of α-chymotrypsin has been studied in the acid pH region and is shown to consist of two distinct equilibrium situations. The first of these, transition Aa→ Ab, is a thermodynamically small structural change and is described by changes in the optical rotatory dispersion. The second, transition I, is a thermodynamically large conformational change which is uniquely described by changes in the ultraviolet absorption spectrum. It is shown that transition I at pH 2.0 is a strongly cooperative, two-state transition and that the thermodynamic behavior is consistent with the Brandts model of protein unfolding. © 1969, American Chemical Society. All rights reserved.