A Study on Subunit Groups of Soybean Protein Extracts under SDS‐PAGE

Abstract Protein extracts of 640 soybean cultivars and landraces, mainly from China and a few from the US, were analyzed for their components and subunits based on distribution patterns of bands with varying molecular weights (MW) under SDS‐PAGE (sodium dodecyl sulfate‐polyacrylamide gel electrophoresis). The number and molecular weight of the bands in SDS‐PAGE varied among materials and showed a tendency of continuous distribution. Accordingly, the SDS‐PAGE patterns of the soybean protein extracts were divided into two regions: the region of bands with MW < 44 KDa and that with MW ≥ 44 KDa. The first region containing mainly 11S proteins was divided into four parts, called subunit groups, i.e. 11S‐1 (14.4–22 KDa), 11S‐2 (22–26 KDa), 11S‐3 (26–34 KDa) and 11S‐4 (34–44 KDa). The second region containing mainly 7S protein was divided into six subunit groups, i.e. 7S‐1 (44–49 KDa), 7S‐2 (49–55 KDa), 7S‐3 (55–67 KDa), 7S‐4 (67–73 KDa), 7S‐5 (73–82 KDa) and 7S‐6 (82–91 KDa). The sum of relative contents of 11S‐1–11S‐4 was obtained as the relative content of 11S protein, those of 7S‐1–7S‐6 as that of 7S protein, and therefore, the 11S/7S ratio obtained. The proposed criteria were demonstrated to be simple, stable and feasible. Among the 640 tested materials, 39 lacked 11S‐1 but none lacked the other 11S subunit groups, while deficiencies existed in all the six subunit groups of 7S, indicating a great potential for the genetic variation of protein components and subunits for breeding for the improvement of protein qualities.