Ether lipids are widespread in animal tissues and, of these, the plasmalogens are the most important. In mammals, ether links are virtually exclusively confined to the choline and ethanolamine glycero-lipid classes.
Although the pathway for the formation of ethanolamine (and choline) plasmalogens uses CDP intermediates, there are several points of difference with those for the synthesis of diacylphos-pholipids. First, the ethanolamine (choline) phosphotransferase enzyme uses a plasmalogenic diacylglycerol (1-alkenyl-2-acyl-sn-glycerol). Hajra and his group showed that the starting point for its synthesis was dihydroxyacetone phosphate (see also Section 126.96.36.199). This compound was acylated, the acyl group at position 1 being substituted by a long-chain alcohol and then the keto group at position 2 reduced. The newly created hydroxyl at sn-2 could then be acylated and the phosphate group removed to produce a plasmalogenic diacylglycerol (Fig. 7.7).
It is interesting to note that the acyldihydroxy-acetone phosphate at the start of the pathway can also be reduced to form lysophosphatidate thus
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