BIOCHEMICAL BASIS OF FLOUR PROPERTIES IN BREAD WHEATS .2. CHANGES IN POLYMERIC PROTEIN-FORMATION AND DOUGH GLUTEN PROPERTIES ASSOCIATED WITH THE LOSS OF LOW M(R) OR HIGH M(R) GLUTENIN SUBUNITS/

Polymeric protein plays a critical role in governing the functional pr operties of wheat flour. Wheat genetic lines lacking high M(r) and, si milarly, low M(r) glutenin subunits from one, two or all three Glu-1 o r Glu-3 loci, respectively, were thus used to investigate the effects of these polypeptides on glutenin polymer formation and dough/gluten p roperties. Polymer formation (quantity, size distribution) was studied by size-exclusion highperformance liquid chromatography (SE-HPLC) usi ng extractable, unextractable and total protein from flour, as well as by diagonal electrophoresis using total protein extracts. The loss of Glu-1 or Glu-3 subunits had significant effects on the quantity of to tal, extractable and unextractable polymeric protein and on the dough and gluten properties of these lines. Dough and gluten properties were significantly correlated with the proportions of both total and unext ractable polymers (a measure of the relative molecular size distributi on of polymeric protein), although more strongly with the proportions of unextractable polymers in the case of Glu-1 null lines. The proport ion of total polymeric protein decreased more markedly when all the Gl u-3 subunits were deleted than when all the Glu-1 subunits were absent , which was in accordance with the relative quantities of these two ty pes of the subunits in the grains. In contrast, loss of all the Glu-1 subunits, on an equal weight basis, reduced the amounts of the larger polymers to a much greater extent than the loss of all the Glu-3 subun its, reflecting more than the molecular size differences in these subu nits. SE-HPLC and diagonal electrophoresis of total protein extracts f rom the triple Glu-1 and Glu-3 null lines also revealed that Glu-1 or Glu-3 subunits form large polymers on their own. When both high and lo w M(r) glutenin subunits were present together, however, the amount of large polymer was much greater than the sum of the amounts when only one group was present, suggesting a positive interaction between these two groups of subunits with respect to polymer formation.