ISOLATION AND CHARACTERIZATION OF CHENOPODIN, THE 11S SEED STORAGE PROTEIN OF QUINOA (CHENOPODIUM-QUINOA)

Quinoa (Chenopodium quinoa), a seed crop from the Andes region of South America, has been reported to have an exceptional seed protein amino acid composition. The purpose of this study was to isolate and characterize a major seed storage protein of quinoa, an 11S-type globulin called chenopodin. Extraction of quinoa seed protein was optimized with regard to extraction time, salt concentration, and buffer volumes. Extraction with 0.5 M NaCl solubilized polypeptides having molecular weights of 8000-9000, 22000-23000, 32000-39000, and 50 000. Enrichment of the chenopodin polypeptides (the A subunit group at 32 000-39 000 and the B subunit group at 22 000-23 000) was achieved by acid precipitation of the extract at pH 5.0. Gel filtration was necessary to purify the native (320 000) chenopodin. The disulfide-bonded A (acidic) and B (basic) polypeptides were separated by denaturation, reduction, and alkylation followed by ion-exchange chromatography. The amino acid compositions of the A and B polypeptides were similar to those of the acidic and basic subunits from other 11S seed globulins. The N-terminal sequence of one of the B polypeptides (GLEETICSARLSENIDDPSKA) was highly homologous to the basic subunits of several other 11S storage proteins, especially to rapeseed cruciferin.