Synthetic pathways for polar lipids. The black arrows indicate the
bacterial and eukaryotic pathway, and the red arrows denote the
archaeal pathway. The red striped arrows show hypothetical steps
in the archaeal pathway. The names or EC numbers in rectangles
indicate the enzymes responsible for the corresponding steps.
Experimentally identified archaeal enzymes are indicated by
characters reverse-printed on red. Bacterial and eukaryotic
enzymes belonging to the CDP alcohol phosphatidyltransferase
family are shown in green rectangles. Enzymes in rectangles with
blue frames are involved in the synthesis of lipids with choline.
Abbreviations: DHAP = dihydroxyacetonephosphate; G3PDH =
sn-glycerol-3-phosphate dehydrogenase; G1PDH =
sn-glycerol-1-phosphate dehydrogenase; G3P =
sn-glycerol-3-phosphate; G1P =
sn-glycerol-1-phosphate; GGGPS, GGGP synthase;
GGGP =
3-O-geranylgeranyl-sn-glycerol
phosphate; DGGGPS, DGGGP synthase; PA, phosphatidic acid; DGGGP =
2,3-di-O-geranylgeranyl-sn-glycerol
phosphate; PCS = phosphatidylcholine synthase; PSS =
phosphatidylserine synthase; ASS = archaetidylserine synthase; PGS
= phosphatidylglycerol synthase; AGS = archaetidylglycerol
synthase; PIS = phosphatidylinositol synthase; AIS =
archaetidylinositol synthase; PC = phosphatidylcholine; PS =
phosphatidylserine; AS = archaetidylserine; PGP =
phosphatidylglycerolphosphate; AGP = archaetidylglycerolphosphate;
PI =phosphatidylinositol; AI = archaetidylinositol; PSD =
phosphatidylserine decarboxylase; ASD = archaetidylserine
decarboxylase; PGPP = PGP phosphatase; PE =
phosphatidylethanolamine; AE = archaetidylethanolamine; PG =
phosphatidylglycerol; and AG = archaetidylglycerol.