CATALYTIC EFFICIENCY OF SIGNAL PEPTIDASE-I OF ESCHERICHIA-COLI IS COMPARABLE TO THAT OF MEMBERS OF THE SERINE-PROTEASE FAMILY

A method for estimating the activity of bacterial signal peptidase I ( SPase I) was used to determine its activation energy (E-act). Pro-OmpA -nuclease A, a hybrid secretory precursor, was purified to homogeneity under denaturing conditions and used as a substrate. This substrate w as used to determine the activity of SPase I at different temperatures . The results show that the conformation of the mature domain of the s ubstrate pro-OmpA-nuclease A has no discernible effect on the activity of SPase I. The activity data at a range of temperatures were then us ed to determine the activation energy using the Arrhenius equation. We have estimated E-act to be 10.4 +/- 0.6 kcal/mol. This work indicates that SPase I is as catalytically efficient as the His-Ser-Asp family of proteases.