FTIR AND NMR-STUDIES ON THE HYDRATION OF A HIGH-M(R) SUBUNIT OF GLUTENIN

The hydration behaviour of a purified high-M(r) subunit of glutenin ha s been studied using Fourier transform infra-red (FTIR) and nuclear ma gnetic resonance (NMR) spectroscopy. The water-insoluble protein was e xamined in an unalkylated form with intermolecular disulfide bonds, an d in a reduced and alkylated (unpolymerized) form. Hydration produced a marked increase in chain mobility, especially above a threshold wate r content of about 37% w/w. NMR experiments also showed that some part s of the chain were held in a much less mobile state, even at higher w ater contents. Little difference could be seen between alkylated and u nalkylated subunits, implying that NMR is sensitive to localized motio ns, but not to any restrictions imposed by disulfide bridges close to the chain ends. FTIR spectra of the protein films have shown that incr easing hydration enables changes to occur in favour of a more extended and beta-sheet-type structure. The changes in secondary structure are very noticeable at water contents corresponding to the NMR mobility t hreshold. The behaviour is influenced by intermolecular interactions. beta-sheet formation is enhanced by the presence of disulfide bonds in the unalkylated samples. There is little evidence of beta-structure ( sheet or extended chain) either in the dry state, where protein-protei n interactions are strongest, or in dilute acetic acid solution, where the interactions are weakest. The balance between protein-protein and protein-water hydrogen-bonding interactions therefore appears to infl uence the formation of beta-sheet and extended chain structures, and t hese may in turn affect the elasticity of high M(r) subunits.