Identification of a Subtilisin-Like Protease in Seeds of Developing Tung Fruits

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Summary A subtilisin-like protease was identified in the low-density microsomal fraction of developing tung seeds. The abundance of the protease changed significantly throughout seed development and showed a direct temporal correlation with accumulation of storage oil. Once storage oil synthesis was complete, the abundance of the protease decreased dramatically. Determination of the N-terminal amino acid sequence revealed that the protease sequence began just after a conserved pro-domain cleavage site, suggesting that the protease was fully active in developing tissue. Extraction of microsomal membranes with high salt or pH demonstrated that the protease was not a membrane-anchored protein.