Cereal Chem 65:95-100   |  VIEW ARTICLE

Studies on Disulfide Bonds in Glutenin.

J. A. D. Ewart. Copyright 1988 by the American Association of Cereal Chemists, Inc. 

Two attempts to measure the average number of interchain disulfide bonds (SS) per chain in glutenin were made. The first was to let reduced glutenin slowly reoxidize in dilute solution to look for oligomers in samples taken at intervals. It was hoped that intrachain SS would form first because they are stabler and because dilution minimized interchain contacts. The appearance of dimer bands would show when interchain SS were starting to form: the SH groups still unoxidized whould then be a measure of interchain SS. Oligomers did not appear as discrete bands, but as marks on the origin and possibly tailing. Oxidation to glutenin was rapid. The tailing that is well known to occur in the electrophoretic patterns of low molecular weight glutenin suggests that there is little preference for specific pairings of subunits, and consequently they are mostly randomly distributed in glutenin molecules. In the other attempt, glutenin was partly reduced, to varying extents, and SH groups were then blocked. Analysis was measured the fraction (tau) of broken SS. The intinsic viscosity [eta]u was determined and plotted against the fraction of SS broken. These two quantities, tau and [eta]u, were calculated from theory, assuming a range of values for the fraction of junctions with two SS in linear glutenin (delta). The theoretical curves were compared with the experimental points by computer, in the hope that delta would be the value giving the best fit. The results were not so clear cut as expected, but delta was unlikely to be greater than 0.3 and could be zero. It was shown that a previous approach to this problem, also based on viscometry, led to a similar conclusion. This means that if glutenin has linear molecules at least two-thirds, and possibly all, the junctions are likely to consist of a single SS. The exponent, nu, in the Mark-Houwink equation ([eta]u = KM nu) for glutenin appears to be about 0.5. A possible way of distinguishing interchain SS when all subunit sequences are known is suggested.