THE NATIVE MOLECULAR-SIZE OF ALKYL-DIHYDROXYACETONEPHOSPHATE SYNTHASEAND DIHYDROXYACETONEPHOSPHATE ACYLTRANSFERASE

Dihydroxyacetonephosphate acyltransferase (DHAP-acyltransferase) and a lkyl-dihydroxyacetonephosphate synthase (alkyl-DHAP synthase) are the first two enzymes involved in the biosynthesis of ether phospholipids. Both peroxisomal enzymes have recently been purified to homogeneity a nd their molecular weights under denaturing conditions were reported. To determine the in situ functional size of both enzymes, radiation in activation experiments were performed. Alkyl-DHAP synthase showed sing le exponential decays, both when enzymatic activity and when immunorea ctive protein levels were measured, from which target sizes of 79 +/- 2 kDa and 78 +/- 4 kDa, respectively, were calculated. DHAP-acyltransf erase activity increased at lower doses and decayed upon further irrad iation with an apparent target size of 62 +/- 7 kDa. We conclude from these data that the functional unit sizes for both enzymes in situ are represented by their single polypeptide chains. (C) 1998 Elsevier Sci ence B.V. All rights reserved.