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Volume 271, Number 52, Issue of December 27, 1996 pp. 33344-33351
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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A Cysteine Protease That Processes Insect Vitellin
PURIFICATION AND PARTIAL CHARACTERIZATION OF THE ENZYME AND THE PROENZYME

(Received for publication, April 12, 1996, and in revised form, October 14, 1996)

From the Department of Biochemistry and Molecular Biology and Graduate Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003

A cysteine protease that initiates degradation of vitellin (Vt) in the orthopteran Blattella germanica, and its proprotease precursor, were purified from yolk and partially characterized. The protease, purified 300-fold, contains three peptides of M_r 27,000, 29,000, and 31,000. A comparison of the purified enzyme's action pattern on Vt in vivo and in vitro confirmed its role in Vt processing. Protease-deficient yolk (day 0 postovulation) contained peptides of M_r 35,500, 37,000, 39,000, and 41,000, which were absent from yolk with protease activity. These were replaced by three peptides of approximately M_r 29,000, at days 2-3, the same time in development that protease expression and acidification of yolk granules occur (Nordin, J. H., Beaudoin, E. L., and Liu, X. (1991) Arch. Insect Biochem. Physiol. 18, 177-192). Acidification of purified proprotease converted it to three peptides of approximately M_r 29,000 with cysteine protease activity. This conversion also required participation of a cysteine protease. Activated proprotease had the same pH activity profile, susceptibility to inhibitors, and cathepsin classification (L) as the protease. These results indicate that the Vt-processing protease is derived from a proprotease, which is activated in vivo by a developmentally regulated decrease in intragranular pH.

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