Re-examination of the Glycosylation of High Mr Subunits of Wheat Glutenin

Abstract

SDS−PAGE-separated high Mr wheat glutenin subunits stained positively in the DIG-glycan procedure, suggesting that they were glycosylated, but control experiments indicated that these were probably false positives. Lack of reaction with concanavalin A indicated the absence of terminal mannose, glucose, or N-acetylglucosamine. GC/MS analysis indicated that A-PAGE-prepared subunits contained glucose, mannose, xylose, and galactose. Because gel regions containing no protein contained similar amounts of those sugars, they were most likely unbound contaminants. RP-HPLC-purified subunits from cv. Apollo wheat contained variable amounts of glucose only, probably representing starch contamination. RP-HPLC-purified subunits 1Ax1 and 1Bx7 contained no GC/MS-detectable sugars even though the procedure was sensitive enough to detect 1 sugar residue per 40 subunit molecules. Mapping of tryptic or chymotryptic peptides, before and after deglycosylation, and GC/MS analysis of isolated tryptic peptides provided no evidence for glycosylation of high Mr subunits. It appears unlikely that high Mr wheat glutenin subunits are glycosylated. Keywords: Wheat; glutenin; glycosylation; subunits