Leucyl β -Naphthylamidase Activities in Developing Seeds and Seedlings of Pisum sativum L

Abstract

The activities of two soluble enzymes which hydrolyse L-leucyl ß-naphthylamide have been measured in extracts from tissues of seeds and seedlings of Pisum sativum L. by using the chelator 1,10-phenanthroline as a selective inhibitor. In all the tissues studied, the phenanthroline-insensitive enzyme contributed the major proportion of the total activity against this substrate. In developing seeds, most of the activity of both enzymes is found in the maturing cotyledons, which develop maximum phenanthroline-sensitive and -insensitive activities respectively of 0.51 and 1.26 µmol per min per cotyledon (cv. Melbourne Market, dwarf) or 0.84 and 1.32 µmol per min per cotyledon (cv. Telephone, tall). In the cotyledons of germinating seeds, both enzyme activities increase within 24 h to values which are substantially lower than the maximum values found during development. These activities are maintained between 1 and 6 days from imbibition then they decline rapidly during the period of maximum rate of removal of protein from the cotyledon. The highest activities of both enzymes occur in tissues which are very active metabolically. This supports the view that they function as aminopeptidases in the general turnover of cellular proteins, rather than playing some additional specific role in the mobilization of storage proteins during germination.