Studies on subunit assembly of broad bean legumin in a reconstitution system

The constituent subunits of 11S globulin of broad bean, legumin, were separated into basic subunits (BS, a mixture of BSI, BSII, and BSIII) and acidic subunits (ASI, ASII, and ASIII). The 11S components were formed in reconstitution reactions from combinations of BS and one or two each of the acidic subunits. The reconstituted 11S components were similar to the native legumin; they all consisted of acidic (A) and basic (B) subunits linked by disulfide bridges in the ratio of 1:1 and had the 6 (AB) structure. In the reconstitution of 11S components, ASI preferentially selected BSI from among the three kinds of BS, and ASII and ASIII exhibited selectivities for BSII and BSIII, respectively. The same selectivities were observed in the reconstitution reaction containing all subunits and in the renaturation reaction from the reduced-denatured state. The selectivity of each acidic subunit for basic subunits coincides with the combination of acidic and basic subunits in the native legumin. The 11S component was reconstituted from any combination of the intermediary subunits examined. This may be one of the reasons for the occurrence of heterogeneity of legumin molecular species.