γ‐Purothionins: amino acid sequence of two polypeptides of a new family of thionins from wheat endosperm

Abstract

Two homologous sulfur-rich basic polypeptides form wheat endosperm, so-called γ₁-purothionin and γ₂-purothionin, are described. Purification involves extraction with volatile solvents and ammonium bicarbonate fractionation followed by reversed-phase high-performance liquid chromatography. The complete primary structure of these two polypeptides has been determined by automatic degradation of the intact, S-carboxymethylated γ-purothionins and peptides obtained by enzymatic cleavage. γ₁-Purothionin and γ₂-purothionin consist of 47 amino acids with an assessed molecular weight of 5239 and 5151 Da, respectively and 8 cysteines organized in 4 disulfide bridges. They present a high degree of homology among themselves (89% of identity) and are the first two thionin-like polypeptides, so-called y-thionins, described from wheat endosperm.