Metabolism of alkyldihydroxyacetone phosphate in rat brain.

Alkyldihydroxyacetone-P is the first detectable product in the biosynthetic pathway for ether-linked glycerolipids that eventually leads to the formation of ethanolamine plasmalogens, a major constituent of myelin. During early postnatal development, the specific activity of NADPH2:alkyldihydroxyacetone-P oxidoreductase in microsomes from rat brain is maximum at 4-5 days after birth, the time when the specific activity of the enzymes that synthesize alkyldihydroxyacetone-P also peaks. For the oxidoreductase assay, we developed a thin-layer chromatographic method that separates alkyldihydroxyacetone-P as the dinitrophenylhydrazine derivative from its reduced product (alkylglycerol-P), with excellent resolution. Phosphohydrolases associated with brain microsomes exhibit optimal pH maximums at 5.2-5.6 and 7.5-7.8 for all three substrates tested -- alkyldihydroxyacetone-P, alkylglycerol-P and alkylacylglycerol-P. Alkylglycerol-P was most readily dephosphorylated under all experimental conditions. The enzyme(s) that dephosphorylates alkyldihydroxyacetone-P and alkylglycerol-P have similar properties with respect to Mg-2+ or EDTA; with both substrates, Mg-2+ had no effect and EDTA was highly stimulatory. In contrast, EDTA strongly inhibited the dephosphorylation of alkylaclglycerol-P and although Mg-2+ (1 mM) appeared to be required for optimal activity, higher levels inhibited the reaction.