Autolysis of beta-trypsin at pH 3.0.

Bovine beta-trypsin was prepared from commercial crystalline trypsin by SP-Sephadex equilibrium chromatography (D.D. Schroeder and E. Shaw, Journal of Biological Chemistry, 243: 2943-2949, 1968) and by a modification which included 0.1 M NaCl in the eluting buffer to reduce the buffer volume (time) required. SDS-PAGE analysis indicated that beta-trypsin prepared by both methods contained appreciable amounts of alpha-trypsin. The following relative amounts of alpha-trypsin were detected at each step of the process: 4.4% eluted from the column into pH 3.0 buffer; 10.7% after concentration on SP-Sephadex; 14.9% after desalting at pH 3.0; 16.1% after lyophilization. These data show that even at pH 3.0, a condition under which trypsin is believed to be inactive, and which is employed for preparation and storage of trypsin solutions, appreciable partial proteolysis can occur to generate the two-chain alpha form from beta-trypsin.