Preliminary crystallographic analysis of sweet potato beta amylase.

Beta amylase from sweet potato has been crystallized in a form suitable for high resolution X-ray diffraction analysis from a mixture of polyethylene glycol 400 and ammonium sulfate at room temperature. The crystals are rectangular prisms and occasionally reach a size of 1 mm on an edge. The space group of the crystals is I422 with cell dimensions of a = b = 196.4 A and c = 72.2 A. There are four tetramers of about M(r) = 210,000 in the unit cell centered at 222 symmetry points. The asymmetric unit is a single beta amylase subunit of about M(r) = 52,000. The tetrameric molecule must have exact 222 molecular symmetry relating its subunits.