Crystallization and preliminary x-ray investigation of soybean beta-amylase

Beta-Amylase [1, 4-alpha-D-glucan maltohydrolase, EC 3.2.1.2] has been purified from defatted soybean meal by fractional precipation with ammonium sulfate, ion-exchange chromatography on CM- and DEAE-Sephadex and gel filtration chromatography on Sephadex G-100. Two different components of beta-amylase were crystallized from ammonium sulfate solutions, and the homogeneity of each preparation was confirmed by sedimentation and disc electrophoretic analyses. Both components of soybean beta-amylase formed large single crystals (trigonal crystal system) from 40--50 per cent saturated ammonium sulfate solution buffered at pH 5.4 on dialyzing concentrated protein solution in the apparatus of Zeppezauer et al. Preliminary X-ray diffraction data gave a hexagonal lattice with unit cell dimensions a=86.1 A and c=144.4 A. The space group corresponds to P3121 or P3221, and one asymmetric unit contains one molecule of beta-amylase, assuming a crystal density of 1.25 g/ml and a molecular weight of the enzyme of 60,000 daltons. In this case, the crystal has a volume of 2.53 A-3 per atomic mass unit, and the percentage of protein in the crystal is about 52.