Comparative investigations of gluten proteins from different wheat species- II. Characterization of omega-gliadins

Flours of different wheat species (common wheats including winter wheat, sp ring wheat, and wheat rye hybrid, spelt, durum wheat, emmer, and einkorn) w ere successively extracted with a salt solution and 60% (v/v) aqueous ethan ol. The alcohol extracts (gliadins) were separated by reversed-phase HPLC. Six to nine different omega -gliadins were obtained for each wheat sample a nd were characterized by their relative amounts, the amino acid composition s, the N-terminal amino acid sequences, and the molecular masses. The wheat s investigated showed typical differences in the qualitative and quantitati ve HPLC patterns. The amino acid compositions of all omega -type gliadins r evealed significantly higher proportions of glutamine, proline, and phenyla lanine compared with other gluten proteins. These three amino acids account ed for 70 to 86% of the total composition. Typical differences in amino aci d compositions, N-terminal sequences, and molecular masses allowed a clear differentiation of the proteins into omega5- and omega1,2-type gliadins; th e gliadin fractions of emmer and einkorn contained only the omega5-type, bu t not the omega1,2-type. omega5-Gliadins were characterized by extremely hi gh proportions of glutamine (52-57 mol %) and relatively high proportions o f proline (18-21 mol %) and phenylalanine (9-10 mol %). omega1,2- Gliadins had less glutamine (39-45 mol %) and phenylalanine (6-8 mol %), but much mo re proline (22-31 mol %). omega5-Gliadins of all wheats except emmer could be assigned to the N-terminal sequence variants SRQLSP or SRLLSP; the typic al sequence of emmer omega5-gliadins was SMELQT. The N-terminal sequences o f omega1,2-gliadins were characterized by two basic variants beginning with KELQSP or ARQLNP. The wheat rye hybrid had additionally components with th e sequence RQLNPS known from omega -secalins of rye. The determination of m olecular masses by MALDI-TOF mass spectrometry revealed a range of 44,000-5 5,000 for the omega5-type and a range of 36,000-44,000 for the omega1,2-typ e. Thus, the actual masses were by far lower than the values derived from S DS-PAGE mobility.