Comparisons of soybean urease isolated from seed and tissue culture.

Urease was purified 500-fold to electrophoretic homogeneity from ground, dry soybeans. Sodium dodecyl sulfate-acrylamide gel electrophoresis indicates a subunit size of 93,500 daltons which is identical with that of jack bean urease. In solutions of high ionic strength, there exists a single urease species (species 1) with a size of about 480,000 daltons based on agarose column chromatography and migration in acrylamide gels. In solutions of lower ionic strength (e.g. 3 nm phosphate), a new lighter species (species 2) predominates which has a size of about 280,000 daltons. Soybean and jack bean urease are serologically related but also contain unique antigenic determinants. The amino acid composition profiles of soybean and jack bean urease show only small differences in the amounts of four amino acids. The urease activity purified from soybean cell suspension cultures was electrophoretically identical with the seed enzyme (both species 1 and species 2 being present in buffers of intermediate ionic strength, viz. 10 mM phosphate). Antibodies to soybean seed urease were purified by affinity chromatography. They were then separated from cross-reacting antibodies to jack bean urease by chromatography over Sepharose 4B containing covalently linked jack bean urease. The effluent antibodies no longer precipitated nor inhibited jack bean urease but inhibited ureases from soybean seed and soybean tissue culture to the same extent. In spite of this immunological evidence for a detailed similarity between soybean seed urease and urease partially purified from suspension culture, urease activity in crude extracts of suspension culture is heterogeneous both with respect to size and affinity for monospecific antiseed urease antibodies.