Separation of alcohol-soluble proteins (zeins) from maize into three fractions by differential solubility

The prolamin of maize (Zea mays L.), zein, was extracted from endosperm meal with 60% (v/v) 2-propanol/1% (v/v) 2-mercaptoethanol either directly or subsequent to extraction with 90% (v/v) 2-propanol. The zein extracted with 90% 2-propanol was essentially made up of 20 to 24 kilodalton polypeptides (alpha-zein) while that extractable with 60% 2-propanol/1% 2-mercaptoethanol contained, in addition to alpha-zein, 17 to 18 kilodalton methionine-rich polypeptides and a 27 kilodalton proline-rich polypeptide. While zein was separated into three fractions by differential solubility in 90% 2-propanol and 30% 2-propanol/30 millimolar sodium acetate (pH 6) using two different fractionation protocols. Each of the three solubility fractions (SF1, SF2, and SF3) had a unique polypeptide composition. Based on results obtained from two inbreds, K55 and W64A, the SF1 constituted 75 to 80% of the total zein and included as major components 20 to 24 kilodalton polypeptides and a minor 10 kilodalton polypeptide. The SF2 made up 10 to 15% of the total zein and included exclusively 17 to 18 kD methionine-rich polypeptides. A 27 kilodalton proline-rich component constituted the SF3 and contributed 5 to 10% to total zein.