Periplasmic proteases of Escherichia coli

In the course of examining the turnover of enzymes and proteins subject to catabolite inhibition and/or catabolite repression in Escherichia coli, we have observed at least three novel calcium- or manganese-activated proteolytic activities restricted to the periplasmic space. The occurrence and level of these proteolytic activities vary with the stage of cell growth and carbon source. Each of these proteases are neutral metalloendoproteases capable of degrading test substrates such as casein, insulin, globin, and protamine and appear to be unique when compared with the known periplasmic proteases in E. coli. One of these proteases (designated protease VII) has been purified to homogeneity and characterized in regard to subunit structure, sensitivity to protease inhibitors and metal ions, and substrate specificity. Immunological and genetic approaches are being employed to determine if these novel proteases arise from a common gene product. The physiological role of these proteases remains to be established.