Conformation of α zeins in solid state by Fourier transform IR

The major maize storage proteins (α zeins) are deposited as an insoluble mass in the protein bodies of the endosperm. Because they are insoluble in water, most structural studies are performed in alcohol solutions. To solve the question raised by several authors about denaturation of the α zein structure by alcohol, we analyze the secondary structure of α zeins prepared with and without solubilization in alcohol (corn gluten meal and protein bodies with high concentrations of α zeins and traces of β zeins). The secondary structures of α zeins are analyzed in the solid state by Fourier transform IR spectroscopy (FTIR) in KBr pellets and solid‐state 13 C‐NMR spectroscopy. The proportion of secondary structures obtained by FTIR of α zeins prepared with and without solubilization in alcohol yield almost identical proportions of α helices and β sheets. The proportion of α helices (43%) agrees with that measured by circular dichroism in an alcohol solution. However, the proportion of β sheets (28%) is higher than the one measured by the same technique. Gluten and protein body samples with high β zein content showed higher β sheet and lower α helix proportions than that obtained for α zein preparations. The solid‐state 13 C‐NMR spectra show the carbonyl peak for the α zeins at δ 176 and for the sample rich in β zeins at δ 172, which demonstrates the presence of a high content of α helices and β sheets, respectively. These results indicate that alcohol solubilization does not affect the conformation of α zeins, validating the secondary structure measurements in solution. © 2003 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy), 2003