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 carboxy-terminal 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 chromat-ography indicated that the protease is active as a monomer. Purified protease was shown to be inhibited by Zn 2+ and Cu 2+ 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