Utilization of an Improved Methodology To Isolate Lupinus albus Conglutins in the Study of Their Sedimentation Coefficients

Methods utilized frequently for the extraction of globulins from legume seeds lead to a considerable loss of these proteins in the albumin fraction due to a partial solubilization of globulins in the albumin extraction medium. The standard procedure to isolate legume seed globulins was modified by (i) including calcium and magnesium in the albumin extraction solution, which completely solubilizes the albumins free of contaminating globulins, and (ii) adding EDTA and EGTA to the globulin extraction solution, which efficiently extract the globulins. Using this modified methodology, Lupinus albus globulins were isolated and subsequently purified, and the main individual globulins, namely α-, β-, and γ-conglutins, were characterized. α- and β-conglutins have been routinely considered as the 11S (or legumin-like) and 7S (or vicilin-like), respectively, protein components of L. albus seeds. Using the total globulin fraction or the purified conglutins on isopycnic sucrose or glycerol density gradient centrifugation performed under low or high ionic strength and on gel filtration techniques, it is proposed that β-conglutin (with a sedimentation coefficient of approximately 11 S) is considerably heavier than α-conglutin (with a sedimentation coefficient of approximately 7 S).