Food Chemistry

15.2 Individual Constituents 685

Fig. 15.7.RP-HPLC of low-molecular (LMW) sub-
units of wheat glutelin of the cultivar Rektor on Nu-
cleosil C 18 (60◦C, aqueous 2-propanol/trifluoroacetic
acid/acetonitrile. After the prolamins, the protein frac-
tion was extracted from the residue with 70% aque-
ous ethanol/0.5% dithioerythritol at pH 7.6and4◦C;
peaks 2–4, 5–7:ω5-,ω 1 ,2-gliadins. Peaks 8–17: LMW
subunits, peaks 20–25:γ-gliadins or related proteins,
according toWieseret al., 1990)

of protein. Recurring sequences with the pep-
tide unit PQQQF evidently start from position 14.
This represents a clear difference to theω1,2-
type, which explains the typical differences in the
amino acid composition of the two subgroups.
Theω5-gliadins have a higher mobility than
theω1,2-gliadins in acidic PAGE and a lower mo-
bility in SDS-PAGE, Mrbeing between 44, 000
and 55,000 (Table 15.14).
In comparison with the ω5-gliadins, ω1,2-
gliadins have lower values for Glx (ca. 43%),
Phe (ca. 7.5%) and Ile (ca. 3%) (Table 15.14).
Most of the other values are higher, especially
the content of Pro (ca. 26%), which is the highest
within the gluten groups of proteins. In the
case of the N-terminal sequences, two basic
variants apparently exist a: ARQLNPSNKELQS;
b: KELQS, which with varying length are
homologous and lead into a recurring sequence.
The variant a was found more frequently in
ω2-gliadins and the variant b more frequently
inω1-gliadins. The N-terminal sequence of the

Table 15.16.N-terminal sequences of the protein

groups of wheat gluten

Position

510

HMW E G E A S R Q L Q C

subunits of E

glutenin G

K

ω5-Gliadins S R L L S P R G K E

Q

ω1,2-Gliadins −−−−−−−−KELQS

ARQLNPSNKE

LMW-sa:SHIPGLERPS

C

LMW-ma: METSHIPGLE

C

α-Gliadins VRVPVPQLQP

F

P

γ-Gliadins NMQVDPSGQV

I

S

A

aThe LMW type is named after the first amino acid in

the sequence, serine (s) or methionine (m).

ω5-gliadins corresponds to that of variant a in

6 positions. The immediately following recurring

sequence consists of the peptide unit PQQPY,

while the dominating recurring peptide unit

in this protein type seems to be the sequence

PQQPFPQQ.

In acidic PAGE,ω1,2-gliadins have the lowest

mobility. The molecular masses are in the range

Mr= 34 , 000 − 44 ,000.

15.2.1.3.3 Low-Molecular Group (α-Gliadins,

γ-Gliadins, LMW Subunits

of Glutenin)

The quantitatively predominant low-molecular

protein group in gluten (Table 15.14) has the

best balanced amino acid composition. Most

of the values lie between those of the high and

intermediate molecular groups. Only the content

of Cys, Val, Met, and Leu is higher (Table 15.15).