PURIFICATION OF A NOVEL TYPE OF SDS-DEPENDENT PROTEASE IN MAIZE USINGA MONOCLONAL-ANTIBODY

A protease which was activated by SDS was purified to homogeneity from maize leaves, On the basis of its proteolytic activity towards ribulo se-1,5-bisphosphate carboxylase/oxygenase (Rubisco) or a synthesized p eptide, the purification was carried out using immunoaffinity chromato graphy with a monoclonal antibody raised against a partially purified enzyme by native gradient PACE, The purified protease showed three ban ds at 40, 15, and 13 kDa on SOS-PACE, indicating that it was composed of heterogeneous subunits, The protease was specifically activated by SDS (optimum = 0.4% for Rubisco proteolysis), but not by poly-L-lysine , fatty acids, or ATP, The protease had a pH optimum around 4.9, beta- Mercaptoethanol stimulated the activity only in the presence of SDS. T he proteolytic activity was sensitive to E-64 and leupeptin hut was re sistant to EDTA, suggesting that the enzyme was an SH-protease, Thus, this enzyme is a novel type of SOS-dependent protease which differs fr om proteasome, matrix metalloproteinase. and other proteases reported in many organisms.