Expression of rat and mouse cathepsin B precursors in Escherichia coli

Vectors for the expression of mouse preprocathepsin B and rat procathepsin B, under the control of a modified lac operon regulatory region, in plasmid pKK233-2 were constructed. In rapidly growing cells induction of preprocathepsin B was cytotoxic. Immune precipitable cathepsin B, compatible in size with that expected for the unglycosylated proenzyme, was produced in both constructs. However, pepsin digestion of extracts did not produce any cathepsin B activity, indicating either that the recombinant forms are not correctly folded or were produced at such low levels that activity could not be detected.