Alkyl dihydroxyacetone phosphate synthase in human fibroblasts and its deficiency in Zellweger syndrome.

Abstract

The cerebro-hepato-renal (Zellweger) syndrome is an autosomal recessive disorder biochemically characterized by the absence of morphologically distinguishable peroxisomes. Key enzymes involved in the biosynthesis of ether phospholipids, i.e., dihydroxyacetone phosphate acyltransferase and alkyl dihydroxyacetone phosphate synthase, are located in mammalian (micro)peroxisomes. We have previously shown a strikingly reduced activity of dihydroxyacetone phosphate acyltransferase in liver, brain, and cultured skin fibroblasts from Zellweger patients (Schutgens et al. 1984. Biochim. Biophys. Res. Commun. 120: 179-184). We have now extended these investigations by studying alkyl dihydroxyacetone phosphate synthase in cultured human skin fibroblasts. Enzymatic activity was determined by measuring the formation of radioactive alkyl dihydroxyacetone phosphate from palmitoyl dihydroxyacetone phosphate and [1-14C]hexadecanol as substrates. The enzyme was optimally active at pH 8.5 and was stimulated (about 2-3-fold) by the presence of 0.05% (v/v) Triton X-100. The apparent KM values for the enzyme in control fibroblasts amounted to 35 microM for palmitoyl dihydroxyacetone phosphate and 90 microM for hexadecanol. The reaction became inhibited at higher concentrations of both Triton X-100 and palmitoyl dihydroxyacetone phosphate. Control skin fibroblasts showed alkyl dihydroxyacetone phosphate synthase activity of 69 +/- 28 pmol X min-1 X mg-1 (n = 7), while fibroblasts from patients had an activity of only 6.3 +/- 1.7 pmol X min-1 X mg-1 (n = 7). Alkyl dihydroxyacetone phosphate synthase was also found to be deficient in tissue homogenates of Zellweger patients. The specific activity of this enzyme in liver, kidney, and brain homogenates from Zellweger patients was less than 15% of that in the corresponding tissues from controls.