a proenzyme, or enzyme precursor, which requires a biochemical change (i.e. hydrolysis) to become an active form of the enzyme.
immunofluorescence microscopy usually shows immune complex deposition with igg and complement in a granular pattern. on electron microscopy, these deposits are semilunar or hump-shaped and are located in the subepithelial area. the presence of these deposits and of small subendothelial and mesangial deposits initiates a complement-mediated inflammatory reaction that leads to glomerular damage. the major antigen is probably zymogen cysteine proteinase exotoxin b (zymogen/spe b). merckmanuals.com