FUNCTIONAL-PROPERTIES OF LOW M(R) WHEAT PROTEINS .1. ISOLATION, CHARACTERIZATION AND COMPARISON WITH OTHER REPORTED LOW M(R) WHEAT PROTEINS

A group of low Mr wheat proteins with characteristic extractability behavior was isolated using two different isolation procedures. The proteins were extractable with water, salt solution and 70% (v/v) ethanol. After water extraction of flour and separation of gluten, a substantial proportion of these proteins was still extractable from gluten using 70% (v/v) ethanol. Based in their amino acid compositions, Mrs and IEF patterns, the isolated proteins resemble closely most of the alpha -amylase/protease inhibitors described in the literature. This was confirmed by enzyme inhibition studies in which it was shown that they inhibited mammalian, but not wheat, bacterial and fungal alpha-amylases. All proteases tested were inhibited by the low Mr proteins. Their Mrs and their high cysteine contents (6·5-8·1 mol%) indicated that the proteins contain four to five disulphide bonds. Free thiol groups were not detected in the proteins. Upon reduction, the Mr increased from 7-8000 to 14-19000. Furthermore, the disulphide bonds were highly reactive as determined by their reaction with the thiol-specific label monobromobimane. This suggests that the low Mr wheat proteins may play a role in thiol group/disulphide bond exchange in wheat proteins. © 1993 Academic Press Limited.