Pumpkin (Cucurbitasp.) seed globulin V. Proteolytic activities involved in globulin degradation in ungerminated seeds

摘要

Two proteolytic activities I and II involved in the globulin degradation were detected in pumpkin seeds. Activity I, hydrolyzingαandβsubunits of the globulin to form Fαβ, was found in both dry seeds and cycloheximide-treated cotyledons, and decreased during germination. Activity II, hydrolyzing Fαβto produce small peptides and amino acids, was not observed in dry seeds but found in cycloheximide-treated cotyledons, increased up to 4 days, and gradually decreased during germination.Activity I gave limited hydrolytic products from the globulin and theγ′chain, but not from Fαβ, theδchain and some animal proteins. It was inhibited by EDTA. On the other hand, activity II hydrolyzed Fαβand theδchain faster than the globulin, theγ′chain and some animal proteins. It was inhibited by EDTA andp-chloromer-curibenzoate, and activated byβ-mercaptoethanol, dithiothreitol and CoCl2. Optimum pH's were at about 6.8 and at 6.0 to 6.8 for activities I and II, respectively.The degradation process of the globulin can be divided into two steps: the first step is the conversion of globulin to Fαβand the second step, Fαβto small pe