Reversibility of denaturation of the zymogen and the proteolyzed zymogen of streptococcal proteinase.

The single, uncross-linked polypeptide chain of the zymogen of the streptococcal proteinase is unfolded to a random structure in 6 M guanidinium chloride. When the denaturing agent is removed by dialysis, the potential enzymatic activity after tryptic hydrolysis and reduction is recoverable in 90% yield. Data on the unfolding process have been obtained by enzymatic assays and by optical rotatory dispersion. The zymogen also refolds after being heated at 100” for 10 min at pH 6.7 or after treatment with 0.1 N HCl for 2 hours at 25”. The proteolyzed zymogen, in which the first 100 residues from the NH, terminus of the parent molecule have been removed, is irreversibly denatured under the same conditions. The NHz-terminal portion of the zymogen is thus necessary for the re-formation of the catalytically active molecule from the fully unfolded chain in this zymogenenzyme system.