Identification of a subtilisin-like protease in seeds of developing tung fruits

A subtilisin-like protease was identified in the low-density microsomal fra ction of developing tung seeds. The abundance of the protease changed signi ficantly throughout seed development and showed a direct temporal correlati on with accumulation of storage oil. Once storage oil synthesis was complet e, the abundance of the protease decreased dramatically. Determination of t he N-terminal amino, acid sequence revealed that the protease sequence bega n just after a conserved pro-domain cleavage site, suggesting that the prot ease was fully active in developing tissue. Extraction of microsomal membra nes with high salt or pH demonstrated that the protease was not a membrane- anchored protein.