Improved method for isolating and quantitating alpha-amino nitrogen as nonprotein, true protein, salt-soluble proteins, zeins, and true glutelins in maize endosperm

The conventional Landry-Moureaux method for selective extraction of maize p roteins was modified by reducing the contact time of meal with extractants and by removing 55% 2-propanol as extractant. The new procedure, coupled wi th a method for quantitating protein at microgram level, was used for asses sing 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 alpha-, beta-, gamma-, and delta-zeins. Proteins extracted subsequen tly with salt plus reductant were minor and poor in lysine (1 mol%). They w ere associated with zeins. Comparison of present data with those available in the literature showed a close similarity for a given genotype between th e percentage of total a-amino nitrogen extracted by 2-propanol plus reducta nt than by salt plus reductant under conditions of the modified procedure a nd 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 quantitatin g cc-amino nitrogen as nonprotein, true protein, salt-soluble proteins, zei ns, and true glutelins in any sample of maize endosperm.