IMMUNOLOGICAL LOCALIZATION AND TISSUE DISTRIBUTION OF ALKYLDIHYDROXYACETONEPHOSPHATE SYNTHASE AND DEFICIENCY OF THE ENZYME IN PEROXISOMAL DISORDERS

Alkyldihydroxyacetonephosphate synthase (alkylglycerone-phosphate synt hase) is a peroxisomal enzyme involved in ether phospholipid biosynthe sis. The recent cloning of the cDNA encoding this enzyme from guinea p ig liver enabled the raising of specific antisera against this enzyme. Both a synthetic peptide corresponding to a predicted epitope and a r ecombinant protein expressed in Escherichia coli were used for that pu rpose. Using western blot techniques, the solubilization of the enzyme From the peroxisomal membrane by Triton X-100 in the presence of salt was confirmed. Neutral hydroxylamine treatment of peroxisomes resulte d in almost no release of the protein from the membrane. The complete polypeptide chain of the enzyme was resistant to proteolysis by trypsi n when intact peroxisomes were studied. Carbonate treatment released a lkyldihydroxyacetonephosphate synthase from the membrane indicating th at the enzyme is not an integral membrane protein. This idea is in acc ord with the absence of a clear hydrophobic transmembrane domain in th e deduced amino acid sequence of the enzyme. Alkyldihydroxyacetonephos phate synthase, as well as its mRNA, could be detected in all five gui nea pig tissues examined. When using the antiserum against guinea pig recombinant alkyldihydroxyacetonephosphate synthase, a cross-reactive protein was detected in a human liver homogenate that runs at a slight ly higher molecular mass. The absence of this band in liver of Zellweg er syndrome and Rhizomelic chondrodysplasia punctata patients provides strong evidence that it represents the human homolog of this enzyme.