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Characterization of Oat Endoproteinases that Hydrolyze Oat Avenins

¹Department of Food Technology, University of Helsinki, POB 27, 00014 University of Helsinki, Finland. ²Corresponding author. Phone: 358-9-191-58638. Fax: 358-9-191-58463. E-mail:markku.mikola@helsinki.fi ³USDA, ARS, Cereal Crops Research Unit, 501 N. Walnut St., Madison WI.

During oat seed germination, the insoluble storage proteins must be solubilized and transported to the embryo for use by the developing plantlet. We showed earlier that pH 6.2 active serine and metalloproteinases were the predominant gelatin-hydrolyzing enzymes of oats, while the oat globulins were degraded by pH 3.8 active cysteine proteases. The pH of the endosperms of germinating oats is 6.2. We have continued our characterization of the germinated oat proteinases by determining which hydrolyze avenins, the oat storage prolamins. Avenins of resting seeds were purified and hydrolyzed with proteinases that were extracted from oat seeds that were germinated for various periods. The peptides released were analyzed using SDS-PAGE. The α-avenins were hydrolyzed at pH 3.8 by cysteine proteinases from four-day germinated seeds and the β-avenins were hydrolyzed by similar enzymes from eight-day germinated seeds. At pH 6.2 or pH 5.0, the avenins were not degraded by any of the germinated oats endoproteinases. It is probable that some kind of pH compartmentalization occurs within germinating oat seed. After four days of germination, either new proteinases form or some preexisting proteinases are activated. The cysteine proteinases are apparently responsible for the majority of the storage protein hydrolysis that occurs during oat germination.