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Identity of High Molecular Weight Gliadin and Ethanol-Soluble Glutenin Subunits of Wheat: Relation to Gluten Structure!

1980; Wiley; Volume: 57; Issue: 6 Linguagem: Inglês

J. A. Bietz, J.S. Wall,

Wheat and Barley Genetics and Pathology

The exact relationship, origin and function of high MW gliadin (HMWG) and ethanol-soluble reduced glutenin (ESRG), 2 heterogeneous wheat protein fractions, are not known. HMWG occurs as small oligomers, soluble in 70% ethanol, whereas ESRG is a disulfide-bonded fraction of glutenin, wheat's highest MW protein class. Upon reduction and alkylation, both fractions are alcohol-soluble, consist of subunits having MW near 44,000 and 36,000, and have similar electrophoretic and chromatographic properties and amino acid compositions. Amino-terminal sequence analyses now prove that many of the same polypeptides comprise HMWG and ESRG. Their N-terminal sequence distribution is H2N-(Val+Asn+Gln+Met)-(His+Gln+Met)-(Ile+Val)-(Pro+Val+Gln)-(Gly+Val+Gln+Asn)-(Leu+Pro)-Gln-(Leu+Gly)-(Pro+Gln+Leu)-(Gln+Pro+Val)-Gln-(Gln+Pro)-(Gln+Pro)-Pro-(Gln+Leu-)Pro-Gln-Gln-. These data imply that many of these polypeptides are homologous and that the heterogeneity of HMWG and ESRG results from duplication and mutation of a common ancestral gene. During biosynthesis, kernel maturation or drying, these polypeptides can combine either with each other to form HMWG or with higher MW ethanol-insoluble polypeptides and with highly aggregating polypeptides to form glutenin. A hypothesis explains how the ethanol-soluble nongliadin polypeptides with 44,000 and 36,000 MW contribute to gluten's structure and to dough's unique viscoelastic properties.