Abstract

When isolated guinea pig liver microsomal membranes were incubated with isomeric (5-, 12-, and 16-doxyl stearoyl) spin-labelled sn-3-[2-3H]phospfaatidic acid in the presence of CTP and Mg2+, formation of corresponding CDP-[2-3H]diglycerides (in an amount representing 16.5–17.4% of the labelled lipids), which were acceptable substrates in the microsomal biosynthesis of sn-3-[2-3H]phosphatidyl-myo-[U-l4C]inositols, took place. When microsomal membranes containing known amounts of labelled CDP-diglycerides were incubated with unlabeled mitochondrial membranes, reisolated mitochondria contained labelled lipids in an amount which could not be accounted for by the microsomal contamination of reisolated mitochondria, determined by the assay of NADPH – cytochrome c reductase activity, establishing therefore the translocation of labelled CDP-diglycerides (and other labelled lipids) from microsomal to mitochondrial membranes in an amount of ~50% of microsomal content. The rate of loss of paramagnetic lipid species in microsomal and in reisolated mitochondrial membranes was found to be quite different. When reisolated mitochondria containing trans-located isomeric spin-labelled CDP-[2-3H]diglycerides were further incubated with sn-3-[U-14C]glycerophosphate, the formation of labelled phosphatidylglycerophosphate and phosphatidylglycerol was detected. These findings established that the translocation of endogenously formed CDP-[2-3H]diglycerides occurred from isolated microsomal membranes to both outer and inner mitochondrial membranes.

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