Cytosol protein-independent translocation of isomeric spin-labelled radioactive lipids from isolated guinea pig liver microsomal to mitochondrial membranes

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Abstract
Intermembranous translocation of membrane-bound radioactive lipids covalently labeled with 5,12- and 16-doxyl stearic acid was studied. Guinea pig liver microsomal membranes containing known amounts of isomeric spin-labeled radioactive phosphatidic acid, phosphatidylcholine and diglycerides were incubated with unlabeled mitochondria; reisolated mitochondria contained around 28-31% of microsomal labeled lipids above the microsomal contamination. The effect of adding crude or pH 5.1 105,000 .times. g cytosol supernatant on the amount and composition of translocated labeled lipids was studied. While the translocation of labeled phosphatidylcholine was slightly stimulated by the addition of these cytosol supernatants, no significant increase of the amount of translocated labeled phosphatidic acid and diglycerides was observed by this addition. A probable mechanism for the cytosol protein-independent translocation of lipids between biological membranes is proposed.