NADPH:alkyl-DHAP oxidoreductase

Fig. 5. Biosynthesis of membrane phospholipids from alkyldihydroxyacetone-P (alkyl-DHAP), the first detectable intermediate formed in the biosynthetic pathway for ether-linked glycerolipids. Enzymes catalyzing the reactions are (1) NADPH alkyl-DHAP oxidoreductase, (II) acyl-CoA 1 -alkyl-2-lyso-sn-glycero-3-phosphate acyltransferase, (III) l-alkyl-2-acyl-in-glycero-3-phosphate phosphohydrolase, (IV) ATP 1-alkyl- /i-glycerol phosphotransferase, (V) CDP-choline l-alkyl-2-acyl-sn-glycerol cholinephosphotransferase (dithiothreitol-sensitive), (VI) CDP-ethanolamine l-alkyl-2-acyI-sn-glycerol ethanolaminephosphotransferase, and (VII) acyl-CoA 1 -alkyl-2-acy 1-OT-glycerol acyltransferase.

DHAP can be diverted from its precursor role in ether lipid synthesis by conversion to jn-glycerol-3-phosphate by NADH glycerol-3-phosphate dehydrogenase. Another bypass that prevents the formation of alkyl-DHAP occurs if the ketone function of acyl-DHAP is first reduced by an NADPH-dependent oxidoreductase, since the product, l-acyl-2-lyso-in-glycerol-3-phosphate, can then be converted only to diacylglycerolipids. The metabolic removal and/or formation of fatty alcohols, DHAP, or acyl-DHAP from the ether lipid precursor pool may control ether lipid synthesis and accumulation. 

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