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Improved Method for Isolating and Quantitating α-Amino Nitrogen as Nonprotein, True Protein, Salt-Soluble Proteins, Zeins, and True Glutelins in Maize Endosperm

¹INRA, Laboratoire de Chimie Biologique, INA - PG, F78850 Thiverval- Grignon. ²Corresponding author. E-mail: landry@platon.grignon.inra.fr Fax: 033 1 30 81 53 73. ³INRA, INA-PG, UPS, Station de Génétique Végétale, Le Moulon, F91190 Gifsur-Yvette.

The conventional Landry-Moureaux method for selective extraction of maize proteins was modified by reducing the contact time of meal with extractants and by removing 55% 2-propanol as extractant. The new procedure, coupled with a method for quantitating protein at microgram level, was used for assessing the nitrogen distribution of four soluble protein fractions present in 100-mg samples of endosperm originating from six maize inbreds and opaque-2 versions. Proteins extracted with 55% 2-propanol plus reductant were made up of α-, β-, γ-, and δ-zeins. Proteins extracted subsequently with salt plus reductant were minor and poor in lysine (1 mol%).They were associated with zeins. Comparison of present data with those available in the literature showed a close similarity for a given genotype between the percentage of total α-amino nitrogen extracted by 2-propanol plus reductant than by salt plus reductant under conditions of the modified procedure and that of total Kjeldhal nitrogen extracted by 2-propanol with and without reductant, and by salt plus reductant, using the conventional procedure. A simplified protocol was described and tested for isolating and quantitating α-amino nitrogen as nonprotein, true protein, salt-soluble proteins, zeins, and true glutelins in any sample of maize endosperm.