Biosynthesis, utilization, and translocation of endogenous isomeric spin-labelled radioactive cytidinediphosphodiglycerides from isolated guinea pig liver microsomal to mitochondrial membranes

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Abstract
When isolated guinea pig liver microsomal membranes were incubated with isomeric (5-, 12-, and 16-doxyl stearoyl) spin-labeled sn-3-[2-3H]phosphatidic 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 labeled lipids), which were acceptable substrates in the microsomal biosynthesis of sn-3-[2-3H]phosphatidyl-myo-[U[uniformly labeled]-14C]inositols, occurred. When microsomal membranes containing known amounts of labeled CDP-diglycerides were incubated with unlabeled mitochondrial membranes, reisolated mitochondria contained labeled 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 labeled CDP-diglycerides (and other labeled lipids) from microsomal to mitochondrial membranes in an amount of .apprx. 50% of microsomal content. The rate of loss of paramagnetic lipid species in microsomal and in reisolated mitochondrial membranes was quite different. When reisolated mitochondria containing translocated isomeric spin-labeled CDP-[2-3H]diglycerides were further incubated with sn-3-[U-14C]glycerophosphate, the formation of labeled phosphatidylglycerophosphate and phosphatidylglycerol was detected. 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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