AN 8 KDA METHIONINE-RICH PROTEIN FROM SOYBEAN (GLYCINE-MAX) COTYLEDON- IDENTIFICATION, PURIFICATION, AND N-TERMINAL SEQUENCE

The genes encoding methionine-rich proteins (MRP) in seeds are candida tes for overexpression to enhance the nutritional quality of legume pr oteins, which are relatively deficient in methionine. Our previous wor k on soybean seed localized the MRP in the albumin fraction, and the p resent work further localized them in the low molecular weight fractio n (LMW) of albumin. Enrichment of the albumin fraction for LMW protein s by heparin-Sepharose affinity chromatography before resolution on 2D SDS-PAGE and labeling of methionine-containing proteins with [1-C-14] iodoacetate resulted in identification of three methionine-rich 8 kDa proteins with different pi values. The most acidic of the three (2D-1) was recovered for amino acid analysis and partial protein sequencing. 2D-1 had 8.6% methionine, 11.4% lysine, and high amounts of glutamic acid and aspartic acid. This work lays the groundwork for cloning of t he gene encoding 2D-1, its eventual overexpression in soybean seed, an d elucidation of a possible biological role for 2D-1 and related prote ins.