W. Seilmeier et al., Comparative investigations of gluten proteins from different wheat species- II. Characterization of omega-gliadins, EUR FOOD RE, 212(3), 2001, pp. 355-363
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.