Storage proteins were extracted from isolated protein bodies from mature seeds of Pisum sativum and separated into one legumin and four vicilin fractions. A comparative study was made of the glycosylation of each fraction and all were found to contain covalently attached carbohydrate at a level of between 0.9 and 1.4% of the protein weight. The carbohydrate composition of the legumin fraction was different from that of the vicilin fractions: the major sugar in legumin was glucose (Glc) with some mannose (Man) and glucosamine (GlcN) while, for all vicilin fractions, Man was the major sugar wlth GlcN, Glc and galactose (Gal) in lesser amounts. There were minor differences in carbohydrate composition between vicilin fractions. Each of the vicilin fractions was further separated by concanavalin A (Con A)-Sepharose 4B chromatography into two fractions. The protein which bound to Con A always contained more carbohydrate than the unbound fraction and, in one vicilin fraction, the unbound protein was not glycosylated. No legumin bound to Con A. Both the 20 and 40 kdalton polypeptides of legumin are glycosylated while the 14 kdalton polypeptide was the major site of glycosylation for all vicilin fractions. One vicilin fraction also has a similar amount of carbohydrate associated with a 50 kdalton polypeptide. Some other polypeptides in the vicilins were glycosylated but to a much lesser extent. These findings are compared to those for other legume storage proteins and their significance in storage protein biosynthesis is discussed.
There have been many physicochemical studies of legumin, one of the major storage globulins isolated from pea seed. The more recent literature values for the molecular weight of this protein are in the range 390 000-420 000. These results are not consistent with the subunit molecular weight of legumin determined by dodecyl sulfate-polyacrylamide gel electrophoresis, if a hexameric model is assumed. We have measured the molecular weight of a highly purified sample of Pisum legumin by meniscus depletion sedimentation equilibrium and have found a value of 350 000 � 10 000. Since the oligomeric protein is homogeneous with respect to molecular weight, the heterogeneity reported for the subunit polypeptides, using various conditions of electrophoresis, presumably reflect differences in charge and amino acid composition. The molecular weight of legumin is significantly greater than the value of 325 000 found for cucurbitin, the equivalent crystalline protein isolated from pumpkin seed.
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