Antigenic relationship of legume seed proteins to the 7S seed storage protein of soybean

Extracts enriched for globulin proteins were prepared from the seeds of a large number of legume species and were tested for homology to antisera prepared against the glycosylated 7S seed storage protein of the soybean (Glycine max). Electrophoretic identification and subsequent analysis of proteins precipitated with 7S antisera was useful at relatively short taxonomic distances, particularly within the tribe Phaseoleae, to which G. max belongs. Glycine and most other members of the subtribe Glycininae are unusual within the Phaseoleae in having high molecular weight ($\text{> 70 000}$ dalton) subunit polypeptides. Seeds from other plants representing other subtribes of the Phaseoleae also contained proteins that cross-reacted with the G. max antisera; the molecular weights of these proteins varied from 30 000 to nearly 90 000 daltons. Homology was detected across a wider range of legume tribes within the subfamily Papilionoideae by enzyme-linked immunosorbent assay (ELISA). The results of these experiments suggest both that the 7S proteins of these tribes are evolutionarily related and that at least some features of these apparently rapidly-evolving proteins are under relatively strong selectional constraint.