Pumpkin (Cucurbita sp.) seed globulin II. Alterations during germination

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Abstract
Alterations in pumpkin seed globulin during germination were examined mainly by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The total protein content of etiolated cotyledons decreased to 32% of the initial content 14 days after germination, and the globulin was rapidly degraded to produce new components with molecular weights of about 40,000 (major component) and 30,000 daltons, which were soluble in a solution with relatively low concentrations of salt at neutral pHs in contrast to insoluble crystalline globulin. The proportion of these soluble proteins to the total amount of protein extracted in 2 M NaCl solution increased rapidly during the period of 2 to 4 days after planting. During this period, the globulin was rapidly degraded with progressive increase of the component of 40,000 daltons. This species was separated into two polypeptide chains with molecular weight of about 20,000 daltons by treatment with sulfhydryl reducing reagent. The soluble fraction preserved oxaloacetate decarboxylase activity. These changes in solubility and subunit structure, and the preservation of the decarboxylase activity of heat stable proteins obtained from etiolated cotyledons are discussed.