Isolation and physicochemical characterization of the half‐unit membranes of oilseed lipid bodies

Abstract

The lipid‐free residue of lipid body membranes was isolated from quiescent peanuts and was physicochemically characterized. The preponderant component of the residue was proteinaceous and consisted of at least two polypeptides according to ultracentrifugation, gel filtration, gel electrophoresis and HPLC. The molecular weight of the principal polypeptide was between 10,000 and 16,000 daltons. Only one antigen, immunochemically unique with respect to other peanut components, was detected. Spectral analyses indicated the presence of a protoheme and revealed conformational modes of β‐sheet and unordered structure but no α‐helix. The amino acid composition was similar to that of an integral membrane polypeptide rather than to those of peripheral membranes or other plant polypeptides. The hydrophobicity, conformation and quantitative content of polypeptides were suitable for the existence of a monolayer at the lipid body‐cytoplasm interface. The results indicated that lipid body coatings physicochemically resemble membranes of intracellular organelles and supported the morphological concept that the coatings are half‐unit biological membranes. Reutilization of lipid body membranes appeared possible after lipid depletion during seed germination.