Presence of thiamine pyrophosphate in mammalian peroxisomes.
BACKGROUND
Thiamine pyrophosphate (TPP) is a cofactor for 2-hydroxyacyl-CoA lyase 1 (HACL1), a peroxisomal enzyme essential for the alpha-oxidation of phytanic acid and 2-hydroxy straight chain fatty acids. So far, HACL1 is the only known peroxisomal TPP-dependent enzyme in mammals. Little is known about the transport of metabolites and cofactors across the peroxisomal membrane and no peroxisomal thiamine or TPP carrier has been identified in mammals yet. This study was undertaken to get a better insight into these issues and to shed light on the role of TPP in peroxisomal metabolism.


RESULTS
Because of the crucial role of the cofactor TPP, we reanalyzed its subcellular localization in rat liver. In addition to the known mitochondrial and cytosolic pools, we demonstrated, for the first time, that peroxisomes contain TPP (177 +/- 2 pmol/mg protein). Subsequently, we verified whether TPP could be synthesized from its precursor thiamine, in situ, by a peroxisomal thiamine pyrophosphokinase (TPK). However, TPK activity was exclusively recovered in the cytosol.


CONCLUSIONS
Our results clearly indicate that mammalian peroxisomes do contain TPP but that no pyrophosphorylation of thiamine occurs in these organelles, implying that thiamine must enter the peroxisome already pyrophosphorylated. Consequently, TPP entry may depend on a specific transport system or, in a bound form, on HACL1 translocation.
Fraccascia
Patrizia
P
Department of Molecular Cell Biology, Division of Pharmacology, LIPIT, Katholieke Universiteit Leuven, O&N1, Leuven, Belgium. patrizia.fraccascia@med.kuleuven.be <patrizia.fraccascia@med.kuleuven.be>
Sniekers
Mieke
M
Casteels
Minne
M
Van Veldhoven
Paul P
PP
D000818:Animals; D001692:Biological Transport; D002451:Cell Compartmentation; D008099:Liver; D020675:Peroxisomes / Q000737:chemistry* / Q000378:metabolism; D010766:Phosphorylation; D051381:Rats; D013835:Thiamine Pyrophosphate / Q000032:analysis* / Q000378:metabolism
D013835:Thiamine Pyrophosphate