Diphosphatidyl glycerol

The mitochondrion has an outer and an inner membrane (Figure 1). The outer membrane contains pores formed from a protein, porin, which allow exchange of molecules with molecular weights up to about 2,000 between the cytosol and the intermembrane space. The inner membrane is extensively invaginated to increase its surface area. It has a different lipid composition from the outer membrane and is rich in the acidic phospholipid cardiolipin (diphosphatidyl-glycerol) which is only found in animal cells in mitochondria. Cardiolipin confers good electrical insulating properties on the inner membrane which is impermeable... 

Cardiolipin or diphosphatidyl glycerol is one of the most ancient membrane phospholipids from phylogenic aspects. It is surprising for such a complex molecule as cardiolipin to have evolved as one of the major membrane lipids in prokaryotics, when steroids such as cholesterol and phytosterols did not. In eukaryotic cells, cardiolipin is exclusively localized within the mitochondria where it is particularly emiched in the outer leaflet of the inner membrane. Even though a molecular structure of cardiolipin has been conserved in entire organisms, its biological significance has escaped attention except in the case of anti-cardiolipin auto-antibodies which are clinically associated with the Wasserman reaction. 

The outer mitochondrial membrane contains monoamine oxidase, cytochrome b5, fatty acyl-CoA synthase, and enzymes of cardiolipin synthesis223 as well as other proteins. Cardiolipin (diphosphatidyl-glycerol Fig. 21-4) is found only in the inner mitochondrial membrane and in bacteria. It is functionally important for several mitochondrial enzymes including cytochrome oxidase and cytochome bc1.22a c It is also... 

The structural formulas of phosphatidyl choline and the other principal phosphoglycerides—namely, phosphatidyl ethanolamine, phosphatidyl serine, phosphatidyl inositol, and diphosphatidyl glycerol—are given in Figure 12.5. 

Phosphatidyl glycerol (which include monophosphatidyl glycerol and diphosphatidyl glycerol or cardiolipin). 

The classification of a phosphatidyl ester depends on the nature of the second alcohol esterified to the phosphoric acid. Some of the most important lipids in this class are phosphatidyl ethanolamine (cephalin), phosphatidyl serine, phosphatidyl choline (lecithin), phosphatidyl inositol, phosphatidyl glycerol, and diphosphatidyl glycerol (cardiolipin) (Figure 8.5). In each of these types of compounds, the nature of the fatty acids in the molecule can vary widely. All... 

Figure 1.5. Correlation between the total amount of protein adsorbed and circulation time before plasma clearance of large unilamellar vesicles (LUVs) containing trace amounts of [3H]cholesteryl-hexadecyl ether administered intravenously in CDl mice at a dose of about 20 pmol of total lipid per 100 g of mouse weight. Results are shown for liposomes containing SM PC ganglioside GMl (72 18 10) (open square), PC CH (55 45) (filled circle), PC CH plant PI (35 45 20) (filled square), SM PC (4 1) (open triangle), PC CH dioleoylphosphatidic acid (DOPA) (35 45 20) (open diamond), and PC CH DPG (35 45 20) (open circle) (SM, sfingomyelin PC, phosphatidyl choline CH, cholesterol PI, phosphatdylinositol DPG, diphosphatidyl glycerol) (data from ref. (55))...

If X = glycerol in Eqnation 10.46a, we have phosphatidyl glycerols (10.51a), and if a further phosphatidyl group is added we get diphosphatidyl glycerols (10.51b). Derivatives of all three types (10.49) have now been isolated from various animal and plant materials. The first of these to be detected was Equation 10.51c in 1942 and this was subseqnently named cardioUpin. Compounds of this kind are closely related to the teichoic acids (below). 

U.E Phosphatidylglvcerol and cardiolipinWhen liposomes containing Isotopically-labelled phosphatidylglvcerol or diphosphatidyl-glycerol (cardiol ioin) were in.iected into rats in vivo, some... 

Dry weight percent of total lipids—excluding pigments. -, Not recorded tr, trace. SL, sulfolipid PC, phosphahdylcholine PG, phosphatidylglycerol PI, phosphatidylinositol PE, phosphatidylethanolamine DPG, diphosphatidyl glycerol or cardiolipin. 

This structure and its absolute configuration have been confirmed by chemical synthesis (Plackett 1964). By analogy, cardiolipin may also be named diphosphatidyl glycerol. Thus cardiolipin has the following structure ... 

Cardiohpin, hrst identihed in beef heart, is also a minor constituent of green plant hpids. Its chemical structure is diphosphatidyl glycerol ... 

Fig. 3.11. HPLC-analysis of soy raw lethicin (according to Sotirhos et al. 1986) 1 Triacylglyc-erols, 2 free fatty acids, 3 phosphatidyl glycerol, 4 cerebrosides, 5 phytosphingosine, 6 diphosphatidyl glycerol, 7 digalactosyldiacyl glycerol, 8 phosphatidyl ethanolamine, 9 phosphatidyl inositol, 10 lysophos-phatidyl ethanolamine, 11 phosphatidic acid, 12 phosphatidyl serine, 13 phosphatidyl choline, 14 lysophos-phatidyl choline...

In rat liver, phosphatidylcholine and phosphatidylethanolamine, the major phospholipid components of the mitochondrial membranes, are synthesized in the endoplasmic reticulum and are transferred to the mitochondria through a protein-mediated carrier mechanism. The mitochondria can synthesize phosphatidic acid, phosphatidylglycerol and diphosphatidyl-glycerol from glycerol-3-phosphate and can also convert phosphatidylserine to phosphatidylethanolamine by decarboxylation. The enzymes for phosphatidic acid synthesis are mainly located in the outer membrane. The details of the way in which these phospholipids become incorporated into the inner and outer mitochondrial membranes have yet to be determined. 

The proportion of lipid to proteins in different kinds of membranes varies greatly. Myelin membrane (which shields the nerve fibre) is at one extreme with a molar ratio of lipid to protein of 9 1, whereas the mitochondrial membrane lies at the other extreme with a i i ratio. Myelin membrane lipid is composed of cholesterol, phosphatidylethanolamine, and cerebrosides (the latter are phosphorus-free condensation products of ethanolamine, fatty acids, and a hexose), whereas mitochondrial membrane lipid consists mainly of phosphatidylethanolamine, lecithin, and cardiolipin (diphosphatidyl glycerol). 

Bacterial membranes. The cytoplasmic membrane of bacteria has both usual and unusual features. When the cell wall is completely hydrolysed by lysozyme, this membrane becomes the outer layer. It is 60-100 A thick and sometimes extends into the cytoplasm as a few simple protrusions (Mitchell and Moyle, 1956b Hughes, 1962). It forms about 10 per cent of the dry weight of the cell and has a lipid content of about 25 per cent. There is usually little lipid elsewhere in the cell. An analysis of the lipid of M. lysodeikticus shows that 80 per cent is phospholipid, which is mainly diphosphatidyl glycerol, but some phosphatidyl inositol is also present. 

The diphosphatidyl glycerol (a GPGPG-lipid) has C-15 branched, aliphatic groups (Macfarlane, 1961). Sterols are completely absent from bacteria. 

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