Other Assays
To assess IgG endopeptidase activity of SeMac, human, mouse or horse IgG (20 μg) was incubated with E. coli lysate containing SeMac proteins or 1 μg purified SeMac or GAS M1 Mac in PBS at 37° for 90 min, and the reaction mixture was analyzed by SDS-PAGE. Western immunoblot analysis, which was performed as described previously [15], was used to assess in vitro SeMac production and the presence of SeMac-specific antibody in the horse and mouse convalescent sera. Culture supernatant proteins of S. equi, which were used to assess the in vitro SeMac production, were prepared by the method of Lei et al. [16].