Activities of Various Peptidases in Cotyledons of Germinating Peanut (Arachis hypogaea)

The activities of several carboxy- and aminopeptidases were assayed in extracts prepared from the cotyledons of resting and germinating peanut seeds as well as from growing and fully differentiated peanut leaves. Carboxypeptidases acting on two carbobenzoxydipeptides Z-Phe-Ala and Z-Ala-Phe at pH 5.2 showed minimal activities in “resting” cotyledons, and only slight increases occurred during 7-day germination at 28°C. In peanut leaves the corresponding activities were quite high, about 20- and 6-fold compared to “germinating” cotyledons. Peptidases acting on Leu-Tyr at pH 8.6 and on Ala-Gly at pH 7.8 were highly active in resting cotyledons, and the activities remained essentially constant during germination; corresponding activities in leaves were much smaller (about 15–25% of those in cotyledons). “Naphthylamidases” hydrolyzing the β-naphthylamides of Phe, Leu, and Arg at pH 7.2, were also highly active in resting cotyledons; during germination the first activity stayed at a constant level while the other two decreased progressively. Leaves showed relatively high activities on Phe-bT-NA and Leu-β-NA but only minimal activity on Arg-β-NA. It is tentatively concluded that the peptidases acting on Leu-Tyr and on Ala-Gly as well as the naphthylamidases function in the mobilization of the reserve proteins of peanut cotyledons during germination. The carboxypeptidases, in contrast, do not seem to play a major role in this process.