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Abstract

The albumin fraction of the cotyledons of Pisum contains two major polypeptides which together make up 34% (17% each) of the total albumin fraction. Both of these albumins (Mr∼8000 and ∼22000) are cotyledon specific proteins. In many Pisum lines the Mr∼22000 fraction resolves into two components on Na-dodecylsulphatepolyacrylamide gels. The Mr∼8000 polypeptide was broken down during germination and early seedling growth, indicating that it functions as a storage protein, while the Mr∼22000 polypeptides were degraded relatively slowly. The level of both of these polypeptides was markedly reduced under sulphur deficiency conditions, the Mr∼22000 components being affected to a lesser extent than the Mr∼8000 component. Consistent with this, when [35S]sodium sulphate was injected into the pedicel of control plants during seed development and albumins were isolated at seed maturity, polypeptides of Mr∼8000 and ∼22000 together accounted for a major proportion of the radioactivity in the total albumin fraction. The abundance and relatively high sulphur content of these two albumins could be significant factors in determining the nutritional value of pea seed proteins.