Figure 3. Hydrolysis of IgA by ZapA. IgA (54 µM) was incubated in 50 mM Tris-HCl and 2 mM CaCl₂, pH 8.0, at 37ºC for 24 h without (panel A) or with (panel B) 28 pM ZapA. The incubation mixtures were analyzed by HPLC as described in Material and Methods.