Purification and Characterisation of Crystalline β‐Amylase from Barley

Pure crystalline β‐amylase was prepared from ungerminated barley in the presence of mercaptoethanol or dithiothreitol. The preparation consists of four isoenzymes with different isoelectric points. The preparation is monodisperse and has a molecular weight of 57200 in sedimentation equilibrium analysis. One mole of the enzyme binds 2.6 moles of p‐chloromercuribenzoate, indicating a minimum of 3 sulfhydryl groups per molecule. The enzyme polymerizes very rapidly through the sulfhydryl groups in the absence of reducing agents. p‐Chloromercuribenzoate inhibits the polymerization and the enzymic activity. The activity can be restored completely with the reducing agents mercaptoethanol or dithiothreitol. The amino acid composition was found to be relatively similar to that of wheat β‐amylases.