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

Two proteolytic activities I and II involved in the globulin degradation were detected in pumpkin seeds. Activity I, hydrolyzing α and β subunits of the globulin to form F_αβ, was found in both dry seeds and cycloheximide-treated cotyledons, and decreased during germination. Activity II, hydrolyzing F_αβ to 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 the $γ′$ chain, but not from F_αβ, the δ chain and some animal proteins. It was inhibited by EDTA. On the other hand, activity II hydrolyzed F_αβ and the δ chain faster than the globulin, the $γ′$ chain and some animal proteins. It was inhibited by EDTA and p-chloromer-curibenzoate, and activated by β-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 F_αβ and the second step, F_αβ to small peptides and amino acids.