The active adenovirus protease is the intact L3 23K protein

The L3 23K protein was isolated from adenovirus type 2 and shown to cleave purified substrates, confirming that this protein is the adenovirus protease. Separate antisera, prepared against the amino- and carboxyterminal regions of the 23K protein react with active protease, demonstrating that, contrary to previous reports, zymogen activation is not involved in the regulation of this enzyme. Molecular exclusion chromatography indicated that the protease is active as a monomer. Purified protease was shown to be inhibited by Zn²⁺ and Cu²⁺ and by some, but not all, recognized cysteine protease inhibitors, indicating participation of a thiol group and providing additional support to the suggestion that regulation of the enzyme involves a form of thiol-disulphide interchange.