Inactivation and stabilization of IgA protease from the human oral bacterium Streptococcus sanguis.

The oral bacterium, Streptococcus sanguis, secretes an extracellular protease which specifically cleaves immunoglobulin A (IgA). During in vitro growth of Strep. sanguis at 37 degrees C the IgA protease was completely inactivated within 2 h. Lowering the growth temperature to 31 degrees C reduced the inactivation rate 50 per cent and a doubling of enzyme yield was obtained. The IgA protease could be stabilized by the presence of whole human saliva, by a low concentration of IgA, or by inhibition of non-specific protease activity. Therefore, the inactivation of IgA protease appeared to be the cumulative result of thermal denaturation and inactivation by non-specific proteases.