Endohydrolysis of (1->4)-alpha-D-glucosidic linkages in polysaccharides containing three or more (1->4)-alpha-linked D-glucose units. Binds 1 Ca(2+) ion per subunit. Binds 1 Cl(-) ion per subunit. Binds to the sea anemone inhibitor helianthamide and magnificamide. The two forms of this enzyme, I and II, show very similar activities, molecular masses, and compositions and differ only in their isoelectric points. As no evidence for two variants were in the cDNA library of PubMed:10082956, it is most likely that isoform I (PPAI) and isoform II (PPAII) are two forms of the same protein. Belongs to the glycosyl hydrolase 13 family.