isolation of mustard
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total storage protein fraction was prepared from mustard (Sinapis alba L.) seeds via isolated protein bodies and characterized by sedimentation, immunological, and electrophoretic techniques. Mustard seed storage protein consists of three fractions (1) a “legumin‐like” 13‐S complex composed of two pairs of disulfide‐linked polypeptides (16.5 + 28.5 kDa and 19.5 + 34 kDa, respectively) and two single polypeptides (18 kDa and 26 kDa), (2) a “vicilin‐like” 9‐S complex composed of two glycoproteins (64 kDa and 77 kDa), and (3) two small polypeptides (10 kDa and 11 kDa) which probably represent the 1.7‐S complex found in other Cruciferae. In contrast to related species, no glycosylated polypeptide was found in the 13‐S complex. Immunological relationships were found between the paired polypeptides of the 13‐S complex but not between polypeptides of the 13‐S complex and polypeptides of the 9‐S complex. Pulse‐chase labeling and in vitro translation of polysomal RNA from young embryos demonstrated that the polypeptides of the 13‐S complex originate from high molecular mass precursors, except for the 18 kDa polypeptide which appears to be synthesized in its final size. The amino‐acid composition of the major polypeptides of the mustard storage protein is given.