Characters of cysteine endopeptidases in wheat endosperms during seed germination and subsequent seedling growth {running title } Characters of cysteine endopeptidases in wheat endosperms

The endopeptidases (EPs) in wheat endosperms during seed germination and subsequent seedling growth were characterized by gradient-polyacrylamide gel electrophoresis with gelatin copolymerized into the gel. Four cysteine EPs (EP1, EP2, EP3 and EP4) were detected in wheat endosperm during the 7d growth after seed imbibition. The results also showed that the activities of all these EPs increased continuously, and EP2 first appeared and had the highest proteolytic activity among the four EPs in this experimental process. The optimum pHs of all the four EPs were at pH 4.0; the optimum temperatures of all these EPs were at 40C. All the four EPs were completely inhibited by 25μM E-64 and hadn’t good thermal stabilities, especially EP1. In addition, all these EPs had different substrate specificities to albumins, globulins, gliadins and glutenins, the main storage proteins of mature wheat endosperms; among them, EP2 had the highest proteolytic activities on globulins, gliadins and glutenins, and might be the most important and specific EP which could be tightly correlated with seedling development.