Extraction and structure studies on corn glutelin proteins

Abstract

Various methods were compared for isolating glutelin from the glutelin-starch residue remaining after extraction of salt-soluble and alcohol-soluble proteins from corn endosperm. Glutelin was prepared best by removing starch from the residue either by extraction with 90% dimethyl sulphoxide or by digestion with α-amylase. Either procedure yielded glutelin as a residue which was insoluble in even the most potent protein solvents and only became soluble upon disulphide cleavage. Its insolubility and its high cystine content indicate that glutelin is present in corn endosperm in the form of a 3-dimensional disulphide cross-linked network. Electrophoresis of the peptide subunits of disulphide-cleaved glutelin shows a range of mobilities between that of zein and the salt-soluble proteins of corn endosperm. NaOH (0.1M) extracted almost all the glutelin from the glutelin-starch residue but degraded the protein, as shown by its diffuse electrophoretic pattern and by loss of cystine and lysine. Aqueous 2-chloroethanol extracted only 30% of the glutelin from the glutelin-starch residue, and gel electrophoresis and amino acid analysis showed that the protein was contaminated with zein.