INTRINSIC FLUORESCENCE AND QUENCHING STUDIES OF GLUTEN PROTEINS

Intrinsic fluorescence and quenching studies of gluten protein extract s and their gel-filtration fractions were used to examine the location and environment of tryptophan residues in wheat gluten. The gluten pr otein was extracted with either 2M sodium thiocyanate (NaSCN), 0.05M a cetic acid (HAC), 3M guanidine hydrochloride (GuHCl), or 3M urea. Samp les for gel filtration were extracted with 2M NaSCN. Stern-Volmer quen ching constants (K(SV) approximately 8) and accessibilities (74-124%) obtained for acrylamide quenching of gluten protein extracts indicated that the majority of the tryptophan residues are located on the surfa ce of these proteins or in easily accessible (polar) regions. Emission maxima near 350 nm (EX = 295 nm) and a lack of change in the magnitud e of Stokes' shift under denaturing conditions (8M GuHCl or 6M urea) s upported this conclusion. Tryptophan residues from both high (glutenin ) and lower (gliadin) molecular weight gel-filtration fractions showed similar results. Accessibilities to acrylamide ranged from 101-114%. Acrylamide and iodide Stern-Volmer quenching constants for the high mo lecular weight fraction (K(SVacryl) = 5.9, K(SVI)- = 1.1) showed value s that were lower than those obtained for the low molecular weight fra ctions (K(SVacryl) = 10.1, K(SVI)- = 2.1), suggesting differences in t he topography of these proteins in the regions in which these residues are located.