Studies on the autocatalytic activation of 

 trypsinogen 



J. F. PECHÈRE AND HANS NEURATH 



Department of Biochemistry, University of Washington, Seattle, Washington 



Recent work on the autocatalytic conversion of trypsinogen to trypsin^ -^ 

 has shown that during the activation, and simultaneously with the appear- 

 ance of tryptic activity, a lysyl-isoleucine bond is broken in the A^-terminal 

 region of the trypsinogen molecule, and that correspondingly increasing 

 amounts of a hexapeptide, having the structure valyl-(aspartyl)4-lysine, can 

 be isolated from the activation mixtures. A similar parellelism has been 

 found to exist between the appearance of enzymatic activity and a decrease 

 in the specific levorotation of the protein.^ While the correlation between 

 these chemical, physical and enzymatic parameters appears to be well estab- 

 lished, the interpretation of these data is not self-evident. Thus, the ques- 

 tion remains how the removal of a small peptide from the iV-terminal region 

 of the single polypeptide chain of trypsinogen can account for the appear- 

 ance of enzymatic activity. In consideration of this problem, attempts were 

 made to establish additional correlations between chemical and physical 

 properties and to look for other events which would help to provide a 

 molecular interpretation for the formation of an enzyme from its inactive 

 precursor. 



Such additional correlations have been recently established by investi- 

 gating the following properties during the activation of trypsinogen : (a) the 

 appearance of trypsin, in the form of soybean-trypsin inhibitor compound, 

 as determined by moving boundary electrophoresis of partial activation 

 mixtures, and (b) measurements of the base consumption during activation, 

 as determined in the Jacobsen-Léonis autotitrator. These were compared with 



(c) the amount of hexapeptide, as isolated chromatographically from the 

 trichloroacetic acid (TCA)-soluble fraction of activation mixtures,^ and with 



(d) the percentage change in optical rotation. ^ All these results are summarized 

 in Fig. 1 . In each of the four diagrams shown in this figure, the percentage 

 change in property during activation is plotted against the time of activa- 

 tion; the solid line represents in each case the appearance of enzymatic 

 activity (benzoyl-L-arginine ethyl ester as substrate), as calculated by the 

 Kunitz equation^ from experimental points (not shown). It is evident that 

 the change in five different chemical or physical properties follows exactly 



