ADENOVIRUS TYPE-2 ENDOPROTEASE - ISOFORMS AND REDOX EFFECTS

The cysteine protease encoded by adenovirus type 2 contains eight cyst eines, some of which are involved in catalysis and enzyme activation, Here we investigated the effects of oxidation, mercaptoethanol, dithio threitol, diamide and protein disulphide isomerase on wild-type and mu tant enzymes, Three isoforms of the enzyme were detected in infected c ells and a fourth in preparations of purified recombinant enzyme, The latter isoform was absent in preparations of enzyme mutated at any of the three conserved cysteines, C-104, C-122 and C-126. Enzyme activity could be stimulated by agents other than the authentic activating pep tide (pVIc), such as cysteamine, though less efficiently, Diamide at l ow concentrations stimulated the activity of the ts1 enzyme, but inhib ited both ts1 and wild-type enzyme at higher concentrations, Protein d isulphide isomerase failed to restore enzyme activity to the oxidized isoform, The present studies in combination with previous results usin g mutants appeared to rule out amino acids C-67, C-122, C-126 and C-12 7, leaving the two remaining semi-conserved C-17 and C-40 and the cons erved C-104 as potential candidates for binding peptide pVIc.