Glycinin and beta-conglycinin are the major storage proteins of soybean and determine the functional properties of soybean proteins. Structure-function relationships of glycinin and P-conglycinin were investigated by using Escherichia coli expression systems. Examination of functional properties of various modified versions of proglycinin A1aB1b suggests that the hydrophobicity of the C-terminal region is probably important for a high emulsifying ability, that the topology of free SH residues is closely related to the heat-induced gel forming ability and that the structural factors suitable for gelation and emulsification properties are quite different. Mutual comparison of functional properties of beta-conglycinin constituent subunits (alpha, alpha' and beta) and the core regions of a and a' indicate that the core regions determine thermal stability and surface hydrophobicity, that the extension regions of alpha and alpha' contribute to high solubility and emulsifying abilities and that the carbohydrate moieties inhibit the formation of heat-induced aggregates. Analyses by chimerization of glycinin and P-conglycinin suggest that structure-function relationships are different between glycinin and beta-conglycinin.