Evidence confirming the existence of a 7S globulin-like storage protein in Amaranthus hypochondriacus seed

The 7S amaranth globulin (‘conamaranthin’) was successfully identified, isolated and purified from the seed of Amaranthus hypochondriacus K343 and physico-chemical properties determined. The 7S globulin was found to exist as a hetero-oligomer with a molecular weight of 186.0 KDa and to be composed of a variety of eight non-convalently linked subunits namely: 90.1, 70.9, 40.0, 37.4, 35.2, 31.2, 23.6, and 15.6 KDa. Structural analysis of this protein using far-UV circular dichroism (CD) revealed that it possessed low levels of α-helical and very high β-sheet secondary fractions whereas near-UV CD measurements revealed that its aromatic amino acids were highly motile within its tertiary structure. The globulin was found to undergo a larger surface charge density change with decrease in pH below its isoelectric point of 5.2–5.8 than with increase in pH above this point. An acid-induced dissociation of its subunits was also noted below its determined isoelectric point. Immunochemical investigation of the 7S globulin with the anti-11S amaranth globulin antibody revealed an approximate 30% homology with its 11S amaranth globulin ‘Amaranthin’ counterpart and to be due to structural not sequential epitope recognition. In summary, this study was instrumental in demonstrating that there are substantial differences between the physico-chemical properties of the amaranth’s 7S and 11S globulins. ©