Characterisation of the major storage proteins of Pisum Sativum L.

Abstract

Several types of purification techniques have been investigated with a view to isolating the storage proteins of Pisum sativum: vicilin and legumin. A third storage protein, distinct from vicilin and legumin, has been purified from seed extracts using a combination of ammonium sulphate fractionation, gel filtration and hydroxylapatite chromatography. Hydroxylapatite chromatography has also been used to show that a protein corresponding to convicilln may be Isolated from Vicla faba. Convicilln has been characterised and its properties compared to those of the other storage proteins. It has been shown by SD8- polyacrylamide gel electrophoresis that convicilin has a subunit mol. wt, of 71,000 and gel filtration studies indicate the mol. wt. of its native form to be 290,000. Convicilin is antigenically dissimilar to legumin, but gives a reaction of identity with vicilin when tested against antibodies raised against both proteins. Convicilin has been so named because of this latter property, Convicilln contains no vicilin subunlts and is clearly separated from vicilin by non- dissociating techniques. Unlike vicilin, convicilin does not interact with concanavalin A, and contains no significant amounts of carbohydrate. Convicilin also differs from vicilin in its amino acid composition, one of the most Important differences being that convicilln contains small amounts of sulphur amino acids, while vicilin contains none. Limited heterogeneity in convicilln has also been demonstrated by isoelectric focussing, N-terminal analysis and CNBr cleavage Changes that occurred in the subunit composition of the storage proteins during pea seed development have been investigated. Two forms of vicilin 50,000 mol, wt. and 47,000 mol. wt. subunits have been detected at early stages. The disappearance of the 47,000 mol. wt. vicilin subunit and appearance of lower mol. wt. vicilin subunits at later stages of development has also been demonstrated. The subunit composition, size and charge of the storage proteins of pea, during germination have been investigated. The storage proteins appear to undergo an initial modification, possibly nicking, and there is depletion of most protein subunits with increasing germination time.