Reduced Soluble Proteins Associated with Maize Endosperm Protein Bodies

Abstract

Endosperm protein bodies from developing maize were purified by discontinuous sucrose gradient centrifugation and the protein content analysed by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAE). Major proteins detected were zein polypeptides plus a component with Mr 28 000 and a doublet around Mr 58 000. These proteins were present only in the protein body fraction of the sucrose gradient. Treatment of protein bodies with the reducing agent dithiothreitol (DTT) in aqueous buffer dissolved the components with Mr 28 000 and 58 000, plus minor ones, but not zein. The reduced soluble proteins were separated by DEAE-Sephacel chromatography into three fractions: two of these contained the component with Mr 28 000, and the third the components around Mr 58 000 plus minor ones. Proteins from the three fractions had characteristic amino acid compositions, markedly different from those of zein polypeptides. Chymotryptic digestion experiments performed on protein bodies under various conditions, and two-dimensional electrophoresis of proteins from protein bodies suggested that the major zein polypeptides, the protein with Mr 28 000 and the other reduced soluble proteins have different native organizations.