Protopectinases are a heterogeneous group of enzymes able to solubilize pectin from the insoluble plant protopectin by restricted depolymerization. Enzymic and acid solubilization of pectin from protopectins obtained from different plant materials are compared. Protopectins were prepared from orange, grapefruit, lemon, apple, pear, peach, red and white grapes, carrot, potato, and sugar beet by sequential washing with water and sodium hexametaphosphate. Substantial differences in the amounts of pectin released by the same enzyme from different protopectins (substrate specificity) and by different enzymes from the same protopectin (enzyme specificity) were evident.