Characterization of oat endoproteinases that hydrolyze oat avenins

During oat seed germination, the insoluble storage proteins must be solubil ized and transported to the embryo for use by the developing plantlet. We s howed earlier that pH 6.2 active serine and metalloproteinases were the pre dominant gelatin-hydrolyzing enzymes of oats, while the oat globulins were degraded by pH 3.8 active cysteine proteases. The pH of the endosperms of g erminating oats is 6.2. We have continued our characterization of the germi nated oat proteinases by determining which hydrolyze avenins, the oat stora ge prolamins. Avenins of resting seeds were purified and hydrolyzed with pr oteinases that were extracted from oat seeds that were germinated for vario us periods. The peptides released were analyzed using SDS-PAGE. The alpha - avenins were hydrolyzed at pH 3.8 by cysteine proteinases from four-day ger minated seeds and the beta -avenins were hydrolyzed by similar enzymes from eight-day germinated seeds. At pH 6.2 or pH 5.0, the avenins were not degr aded by any of the germinated oats endoproteinases. It is probable that som e 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 responsi ble for the majority of the storage protein hydrolysis that occurs during o at germination.