Identification, purification and characterization of an acetoacetyl-CoA thiolase from rat liver peroxisomes

Acetoacetyl-CoA specific thiolases catalyse the cleavage of acetoacetyl-CoA into two molecules of acetyl-CoA and the synthesis (reverse reaction) of a cetoacetyl-CoA. The formation of acetoacetyl-CoA is the first step in chole sterol and ketone body synthesis. In this report we describe the identifica tion of a novel acetoacetyl-CoA thiolase and its purification from isolated rat liver peroxisomes by column chromatography. The enzyme, which is a hom otetramer with a subunit molecular mass of 42 kDa, could be distinguished f rom the cytosolic and mitochondrial acetoacetyl-CoA thiolases by its chroma tographic behaviour, kinetic characteristics and partial internal amino-aci d sequences. The enzyme did not catalyse the cleavage of medium or long cha in 3-oxoacyl-CoAs. The enzyme cross-reacted with polyclonal antibodies rais ed against cytosolic acetoacetyl-CoA thiolase. The latter property was expl oited to confirm the peroxisomal localization of the novel thiolase in subc ellular fractionation experiments. The peroxisomal acetoacetyl-CoA thiolase most probably catalyses the first reaction in peroxisomal cholesterol and dolichol synthesis. In addition, it s presence in peroxisomes along with the other enzymes of the ketogenic pat hway indicates that the ketogenic potential of peroxisomes needs to be re-e valuated.