PHOSPHOLIPID-COMPOSITION OF HIGHLY PURIFIED MITOCHONDRIAL OUTER MEMBRANES OF RAT-LIVER AND NEUROSPORA-CRASSA - IS CARDIOLIPIN PRESENT IN THE MITOCHONDRIAL OUTER-MEMBRANE

Isolated mitochondrial outer membrane vesicles (OMV) are a suitable sy stem for studying various functions of the mitochondrial outer membran e. For studies on mitochondrial lipid import as well as for studies on the role of lipids in processes occurring in the outer membrane, know ledge of the phospholipid composition of the outer membrane is indispe nsable. Recently, a mild subfractionation procedure was described for the isolation of highly purified OMV from mitochondria of Neurospora c rassa (Mayer, A., Lill, R. and Neupert, W. (1993) J. Cell Biol. 121, 1 233-1243). This procedure, which consists of swelling and mechanical d isruption of mitochondria followed by two steps of sucrose density gra dient centrifugation, was adapted for the isolation of OMV from rat li ver mitochondria. Using the appropriate enzyme markers it is shown tha t the resulting OMV are obtained in a yield of 25%, and that their pur ity is superior to that of previous OMV preparations. Analysis of the phospholipid composition of the OMV showed that phosphatidylcholine, p hosphatidylethanolamine and phosphatidylinositol are the major phospho lipid constituents, and that cardiolipin is only present in trace amou nts. The phospholipid composition is very similar to that of the highl y purified OMV from mitochondria of Neurospora crassa, although the la tter still contain a small amount of cardiolipin.