Enrichment of proteinase activity in deteriosomes, a new class of microvesicles

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Abstract
Non‐sedimentable microvesicles, termed deteriosomes, have been isolated from the cytosol of bean cotyledons by ultrafiltration, and found to be enzymatically active. Specifically, they possess proteinase activity that is able to catabolize exogenous proteins as well as deteriosome proteins. The proteolytic activity is inhibited by heat‐denaturation and known proteinase inhibitors (iodoacetate and phenylmethylsulfonyl fluoride), and the pattern of deteriosome‐associated proteinase activity changes with advancing senescence of the cotyledon tissue. Deteriosomes are formed by blebbing from membranes. The finding that they possess proteinase activity is consistent with an earlier proposal [(1991) Proc. Natl. Acad. Sci., USA 88, 2269‐2273] that they are involved in membrane turnover and serve as a vehicle for moving bilayer‐destabilizing phospholipid and protein catabolites out of membranes into the cytosol for further processing. The data also indicate that a significant proportion of the proteinase activity traditionally considered to be cytosolic is associated with deteriosomes.