The lack of a phospholipid-exchange-protein activity in soluble fractions of Spinacia oleracea leaves.

When 14C-labelled liposomes prepared from Spinacia oleracea leaf lipids or 14C-labelled microsomal fraction ('microsomes') prepared from Spinacia oleracea leaf protoplasts were incubated with unlabelled intact chloroplasts, there was a considerable transfer of label to the chloroplasts. This transfer occurred in the absence of added protein, but was stimulated by soluble protein fractions from Spinacia oleracea leaves. The stimulation was heat-stable and decreased after dialysis of the protein fractions. Salt solutions, containing no protein, stimulated lipid transfer proportionally to their conductivity. In all cases, the lipid transfer was not protein-dependent, but rather resulted from the fusion of 14C- and 3H-labelled liposomes or microsomes with chloroplasts. It is proposed that this photosynthetic tissue contains no detectable lipid-exchange activity between liposomes, microsomes and chloroplasts and that lipid transfer between these organelles is achieved by non-protein-dependent means.