Summary: β-Amylase hydrolyzes the α-(1,4) glucan linkages in polysaccharides of three or more α-(1,4) linked D-glucose units. Natural substrates such as starch and glycogen are broken down into glucose and maltose. Pure, crystalline β-amylase preparation consists of four isoenzymes with different isoelectric points. The enzyme polymerizes very rapidly through the sulfhydryl groups in the absence of reducing agents. p-Chloromercuribenzoate inhibits the polymerization and the enzymatic activity. The reducing agents mercaptoethanol or dithiothreitol can completely restore the activity.