In vitro polymerization of wheat glutenin subunits with inorganic oxidizing agents. II. Stepwise oxidation of low molecular weight glutenin subunits and a mixture of high and low molecular weight glutenin subunits
High and low molecular weight glutenin subunits (HMW-GS and LMW-GS) were isolated from wheat flour. LMW-GS and a 1:2 (w/w) mixture of HMW-GS and LMW-GS were polymerized in vitro at pH 3.0 by stepwise oxidation with different oxidants (KBrO3, KIO3, H2O2). In analogy with the oxidation of HMW-GS, KBrO3 produced smaller polymers for LMW-GS than KIO3 or H2O2. While similar average sizes were found with flow-field flow fractionation for LMW-GS polymerized with KIO3 and H2O2, multilayer SDS-PAGE and size exclusion HPLC indicated that size distributions were different. Significantly fewer monomers remained after polymerization of LMW-GS than with HMW-GS. The higher polymerization efficiency of LMW-GS was also obvious during polymerization of a mixture of HMW-GS and LMW-GS. Mixed polymerization of HMW-GS and LMW-GS had no observable effect on the polymer size. Multilayer SDS-PAGE of remaining monomers during polymerization revealed differences in polymerizing efficiency between structurally different glutenin subunits, with x-type HMW-GS and B-LMW-GS showing higher degrees of incorporation than y-type HMW-GS and C-LMW-GS, respectively.