The separate incorporation of amino acids into storage and soluble proteins catalysed by two independent systems isolated from developing wheat endosperm

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Abstract
The characteristics of the incorporation of C14-labelled amino acids into the storage and soluble proteins of wheat endosperm were investigated by using isolated endosperm, cell-free homogenates, and isolated cellular components. With homogenates of endosperm tissue the C14-labelled amino acids incorporated into both the storage and soluble proteins were retained after dialysis against water and against solutions of amino acids, and after further incubation with nonlabelled amino acids. The incorporation of C14-labelled amino acids was relatively specific for each amino acid. The incorporation of C14-labelled amino acids into the storage proteins catalysed by the protein-body preparation did not require the addition of ATP or of amino acids. Incorporation was inhibited by heating, and by the addition of urea, mercuric chloride, chloramphenicol, or puromycin. There was no inhibition with actinomycin D or fluoroacetate. The incorporation of C14-labelled amino acids into the soluble proteins catalysed by the supernatant preparation did not depend on the addition of ATP or of other amino acids, but was inhibited by heating and by the addition of urea, mercuric chloride, or chloramphenicol. The radioactivity incorporated into the storage and soluble proteins by the isolated preparations was not confined to the N- or C-terminal amino acid residues, and remained associated with the protein components that were separated by starch-gel electrophoresis. The implication of these findings in relation to the independent synthesis of the storage and soluble proteins of wheat endosperm is discussed.