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Metabolism and Enzymology

Initiation of the Degradation of the Soybean Kunitz and Bowman-Birk Trypsin Inhibitors by a Cysteine Protease ¹

Department of Biological Sciences, State University of New York at Binghamton, Binghamton, New York 13902-6000

Protease K1 activity initiates the degradation of the Kunitz soybean trypsin inhibitor (KSTI) during germination and early seedling growth. This enzyme was purified nearly 1300-fold from the cotyledons of 4-day-old soybean (Glycine max [L.] Merrill) seedlings. Protease K1 is a cysteine protease with a molecular weight of approximately 29,000. It cleaves the native form of KSTI, Ti^a, to Ti^a_m, the same modified form observed in vivo. In addition to attacking KSTI, protease K1 is also active toward the major Bowman-Birk soybean trypsin inhibitor, as well as the , ', and subunits of soybean -conglycinin. The properties and temporal variation of protease K1 during germination indicate that it is responsible for initiating the degradation of both KSTI and Bowman-Birk soybean trypsin inhibitor in the soybean cotyledon.

¹ Supported by National Science Foundation grant PCM 8301202.