Three forms of polygalacturonase (PG), designated PG-I, PG-II, and PG-III, were purified to homogeneity from culture filtrate of Penicillium italicum. PG-I was characterized as an exoenzyme, whereas PG-II and PG-III wee characterized as endoenzymes. All three enzymes were present in orange peel infected by P. italicum. Exo-PG-I was the predominant enzyme in infected tissue and constituted 69% of the total PG activity as compared with 4% in the culture filtrate. Endo-PG-II and endo-PG-III constituted only 24 and 7%, respectively, of the activity in the infected tissues, as compared with 71 and 25% in culture filtrate (...)