Translocation of isomeric spin-labelled radioactive cytidinediphosphodiglycerides from isolated guinea pig liver microsomal to mitochondrial membranes

Abstract

Translocation of membrane-bound isomeric (5-, 12-, and 16-doxyl) spin-labelled radioactive cytidinediphosphodiglycerides (CDP-diglycerides) from guinea pig liver microsomal membranes to mitochondrial membranes was studied. When microsomal membranes containing known amounts of isomeric spin-labelled radioactive CDP-diglycerides were incubated with unlabelled mitochondrial membranes, reisolated mitochondria contained labelled lipids in an amount which could not be accounted for by microsomal contamination, indicating that translocation of labelled CDP-diglycerides from microsomal to mitochondrial membranes had occurred. The rate of loss of paramagnetism in microsomal and in reisolated mitochondrial membranes was found to be different, supporting the conclusion that the translocation of labelled lipids between membranes took place. When reisolated mitochondria containing translocated isomeric spin-labelled radioactive CDP-diglycerides were further incubated with sn-3-glycerophosphate, the formation of labelled phosphatidylglycerol was detected. Data from these studies established that the translocation of labelled CDP-diglycerides from microsomal membranes to both outer and inner mitochondrial membranes had occurred.This study established that the isolated guinea pig liver mitochondria are capable of biosynthesis of polyglycerophosphatides (phosphatidylglycerolphosphate, phosphatidylglycerol, and diphosphatidylglycerol or cardiolipin) but depend on the microsomal supply of CDP-diglyceride, an obligatory precursor in the formation of polyglycerophosphatides. This liponucleotide can be translocated, as shown here, to outer and inner mitochondrial membranes for further biosynthetic utilization.