Optical Rotatory Dispersion, Circular Dichroism, and Infrared Studies of Wheat Gluten Proteins in Various Solventsl

The influence of various solvents upon the conformation of gluten proteins, glutenin and gliadin, has been studied by optical rotatory dispersion (ORD), circular dichroism (CD), and infrared (lR) absorption measurements. From ORD data an alpha-helix content of 38% has been calculated for gliadin in trifluoroethanol; 35% for glutenin. Conversely, little or no alpha-helix was found when the proteins were dispersed in 8M urea solutions. CD measurements made on gliadin and glutenin showed the presence of alpha-helical structure. IR absorption spectra of gliadin indicated the presence of alpha-helical and unordered conformations. Conformation of wheat gluten proteins in 3M urea, hydrocWoric and acetic acids, and aluminum lactate systems from optical rotatory disperson (ORD) data has already been reported (1,2,3). In terms of Moffitt-Yang, Cotton effect, and Shechter-Blout calculations, both gliadin and glutenin are likely a mixture of alpha-helix and unordered structures; however, gliadin contains more alpha-helix than glutenin. Further, with an increase in ionic strength, there is an increase in helical content for glutenin but no significant change for gliadin. ORD studies of gluten, glutenin, and gliadin showed that the amount of alpha-helix in each protein is solvent dependent. Since a comprehensive study of the conformation of a protein in solution requires a variety of solvents including helixand random structure-forming ones and, furthermore, since infrared (IR) and circular dichroism (CD) data are desirable in addition to ORD in such a study, ORD, IR, and CD results of gliadin and glutenin in various solvent systems are detailed here. lContribution from the Northern Regional Research Laboratory. a laboratory of the Northern Utilization Research and Development Division, Agricultural Research Service, U.S. Department of Agriculture, Peoria. ill 61604. Reference to a company or product name does not imply approval or recommendation by the U.S. Department of Agriculture to the exclusion of others that may be comparable. Copyright © 1971 American Association of Cereal Chemists, Inc., 1821 University Avenue, St. Paul, Minnesota 55104. All rights reserved,