Disulphide bonds in wheat gluten: isolation of a cystine peptide from glutenin.

Gluten from the wheat variety Rektor was extracted with 70% aqueous ethanol. The residual protein (glutenin) was hydrolysed with trypsin. The partial hydrolysate was separated into seven fractions by gel permeation chromatography on Sephadex G 25. Four cystine-containing peptides were isolated from fraction 5 by reversed-phase high-performance liquid chromatography on ODS-Hypersil. The cystine peptides were detected by differential chromatography of the non-reduced and the reduced samples. The primary structure of the peptides was solved by the Edman degradation reaction and by partial hydrolysis with thermolysin. Three peptides derive from the alpha 2- and beta-purothionins. The structure of the fourth peptide was determined as (Formula; see text) This sequence corresponds to positions 44-48 of known sequences of the high molecular weight (HMW) subunits 9, 10, and 12. Since Rektor contains the HMW subunits 9 and 10, it could be concluded that two HMW subunits 9 or 10, or one subunit 9 and one subunit 10 were linked parallel via two disulphide bridges.