The Carbohydrate of Storage Glycoproteins From Seeds of Pisum sativum: Characterization and Distribution on Component Polypeptides

Abstract

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.