Determination of the number of cysteine residues in high molecular weight subunits of wheat glutenin

A simple method allowing the determination of the number of cysteine residues of the high molecular weight glutenin subunits (HMW-GS) is presented. The method was adapted from that of Creighton (T. E. Creighton, Nature 1980, 2840, 487–489) with modified reagents for alkylation of the cysteine residues and the electrophoretic system. The acid-urea-polyacrylamide gel electrophoresis (PAGE) method, developed by Morel (M. H. Morel, Cereal Chem. 1994, 713, 238–242), was adopted and mixtures of iodoacetic acid and 4-vinylpyridine were used to alkylate the glutenin subunits. The accuracy of the method was checked with some HMW-GS whose number of cysteine residues was already known from molecular biology approaches. In subunits 5*, 2.2, 2.2* and 4.1 (of Dx types) from cultivars Ben and Fiorello, MG 7249, MG 315, and Kador, respectively, only 4 cysteine residues were demonstrated. Subunit 20 was found to exist as a regular Bx and By subunit pair, with the Bx subunit containing only 2 cysteine residues, which is unusual.