Alkyl-dihydroxyacetonephosphate synthase (
alkyl-DHAP synthase) is a peroxisomal
enzyme that plays a key role in
ether phospholipid biosynthesis. To determine the turnover of
alkyl-DHAP synthase in several
peroxisomal disorders, pulse-chase experiments were performed. In control fibroblasts, mature
alkyl-DHAP synthase displayed a half-life of 23 +/- 12 h. In
Zellweger syndrome and
rhizomelic chondrodysplasia punctata fibroblast cell lines, in which
alkyl-DHAP synthase cannot be imported into peroxisomes, the
enzyme was mainly detected in its precursor form. This precursor form showed a much shorter half-life, 5 +/- 2 h. In contrast, when the precursor
protein accumulated inside the peroxisome of a particular
neonatal adrenoleukodystrophy cell line in which processing does not take place, a half-life of 18 +/- 8 h, resembling that of the mature
protein in controls, was observed. In a cell line from a patient with a single deficiency in the activity of
alkyl-DHAP synthase, the mature form was detected and its radioactivity decreased with a half-life of 16 +/- 7 h. Collectively, these results provide an explanation for the instability of
alkyl-DHAP synthase outside its target organelle. Additionally, they indicate that both the precursor and mature form of
alkyl-DHAP synthase exhibit considerable intraperoxisomal turnover.