Abstract
Dihydroxyacetone phosphate acyl transferase (DHAP-AT), alkyl dihydroxyacetone phosphate synthase (alkyl-DHAP-synthase), and glycerol-3-phosphate acyltransferase (GPAT) activities were investigated under optimal assay conditions using highly purified organelle preparations. The data presented clearly indicate that GPAT activity was mainly localized in mitochondria and microsomes, whereas DHAP-AT and alkyl-DHAP-synthase activities were exclusively localized in peroxisomes. A small fraction of the total DHAP-AT and alkyl-DHAP-synthase activities observed in purified mitochondrial preparations was due to the presence of intact peroxisomes. DHAP-AT and alkyl-DHAP-synthase activities were very low in purified microsomes (< 1% compared to peroxisomes) and these activities are thought to be due to sedimentation of peroxisomal fragments (generated during homogenization of liver and processing of liver homogenate) with microsomes. The results indicate that the dihydroxyacetone phosphate pathway does not contribute to the synthesis of glycerolipids other than ether lipids in rat liver. The ether bond formation occurs exclusively in peroxisomes, and all the biosynthetic reactions for plasmalogen synthesis may also be operating within peroxisomes in rat liver.
Highlights
Dihydroxyacetone phosphate acyl transferase (DHAP-AT), alkyl dihydroxyacetone phosphate synthase, and glycerol-3-phosphate acyltransferase (GPAT) activities were investigated under optimal assay conditions using highly purified organelle preparations
The DHAP-AT and alkyl-DHAP-synthase activities detected in purified mitochondrial preparations could be due to the presence of peroxisomes
1% compared to purified peroxisomes, it indicates that liver mitochondria lack both of the enzymes involved in ether lipid biosynthesis
Summary
Dihydroxyacetone phosphate acyl transferase (DHAP-AT), alkyl dihydroxyacetone phosphate synthase (alkylDHAP-synthase), and glycerol-3-phosphate acyltransferase (GPAT) activities were investigated under optimal assay conditions using highly purified organelle preparations. During the past 13 years both DHAP-AT and alkylDHAP-synthase activities have been found to sediment with peroxisomal-enriched fractions of rat or guinea pig liver [9,10,11,12,13,14,15]. DHAP-AT [15, 18,19,20] and alkylDHAP-synthase [15, 19,20,21] activities are deficient in Zellweger syndrome skin fibroblasts. Significant ether lipid biosynthesis is detected in Zellweger syndrome skin fibroblasts [22,23,24]. A significant level of ether lipids is present in liver and skin fibroblasts of Zellweger syndrome patients [16, 17, 24]. In view of the absence of normal peroxisomes in Zellweger patients, the above findings suggest that some ether
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