CHARACTERIZATION OF LOW-MOLECULAR-WEIGHT GLUTENIN SUBUNITS IN DURUM-WHEAT BY REVERSED-PHASE HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY AND N-TERMINAL SEQUENCING

Low molecular weight glutenin subunits (LMW-GS) from a residue prepara tion were fractionated by reversed-phase high-performance liquid chrom atography (RP-HPLC) of reduced subunits from two biotypes of the Itali an durum wheat cultivar Lira that differ at the Gli-Bl/Glu-B3 loci, s uch that Lira 42 has the LMW-1 pattern (associated with poor quality) and Lira 45 has the LMW-2 pattern (associated with good quality) of LM W-GS. N-terminal amino acid sequencing was conducted on the major prot ein fractions (peaks) that differed chromatographically between the tw o types. The fractions included four types of LMW-GS on the basis of t heir N-terminal sequences, which differed in their proportions among t he various fractions. These N-terminal sequences corresponded to the S er-His-Ile-(LMW-s) type, the Met-Glu-Thr-(LMW-m) type, the alpha-(glia din) type, and the gamma-(gliadin) type. The LMW-s type was strongly p redominant in the Lira 45 preparation and predominant in the Lira 42 p reparation. The LMW-m type was next most important in the Lira 45 prep arations, but in the Lira 42 preparations, the percentage of alpha-typ e sequence was higher than the LMW-m type. Both alpha-type and gamma-t ype sequences were stronger in Lira 42 than they were in Lira 45. Resu lts indicated that differences in quality between the Lira biotypes ma y derive from: 1) the relative predominance in Lira 45 glutenins of th e LMW-s type and the LMW-m type subunits, probably acting as glutenin polymer chain extenders; 2) the high proportion of the alpha-type and gamma-type glutenin subunits in the Lira 42 glutenins, probably includ ed in the glutenin polymers because they have an odd number of cystein es and act as glutenin polymer chain terminators; 3) the absolute amou nt of LMW glutenins, which is greater for LMW-2; or 4) some combinatio n of these factors.