Membranes of Protein Bodies. I. Isolation from Cotyledons of Germinating Cucumber Seeds

Protein bodies were prepared from cotyledons of germinating seeds of cucumber (Cucumis sativus) in different ways: the organelles either obtained from protoplasts by lysis or from cotyledons by mechanical disintegration were separated on sucrose-density gradients. In addition, a non-aqueous procedure was employed to isolate protein bodies. Marker proteins indicative of membranes of other organelles were carefully assayed. By this means contaminations in the purified protein-body fractions could be ruled out. Isolated protein bodies were separated into crystalloids, matrix, and membranes. The membranes were purified and characterized according to their equilibrium density (rho = 1.20 kg/l) on sucrose gradients by flotation or sedimentation. Protein-body membranes labelled in the phospholipid moiety were prepared and analyzed after application of [methyl-14C] choline or [32P] phosphate in vivo.