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Comparison of peptides from wheat gliadin and glutenin

Bietz, J.A., Rothfus, J.A.
Cereal chemistry 1970 v.47 no.4 pp. 381
wheat, wheat gluten, gliadin, enzymatic hydrolysis, pepsin, peptides, molecular weight, ion exchange chromatography
Peptic hydrolysis of gluten proteins is rapid at pH 1.8. Concomitant increases in alpha-amino groups suggest that peptides from gliadin and glutenin have respective average mol. wt. of 1990 and 1150. Gel filtration, however, shows that the bulk of each digest contains peptides with apparent mol. wt. >2000. Size distribution of glutenin peptides is different from that of gliadin peptides. Evidently larger peptide segments occur between pepsin-susceptible bonds in glutenin than in gliadin. Additional pepsin-susceptible bonds are exposed in S-aminoethylgliadin, but reduction and S-aminoethylation produce little change in the digestion of glutenin. Similarities between peptide maps from cation- and anion-exchange chromatography of digests of gliadin, glutenin, and their derivatives suggest that most gluten proteins contain segments of polypeptide sequence that are similar or identical. Gliadin peptides eluted from cation-exchange resins at pH 1.8 are especially rich in glutamic acid and proline but are noticeably deficient in lysine, arginine, cystine, and methionine. Corresponding peptides from glutenin are also rich in glutamic acid and proline; in addition, they contain significant amounts of glycine and cystine. The greatest difference between gliadin and glutenin may reside in peptides that are largely ninhydrin-negative.