Three human enzymes can utilise ketone bodies for energy production. Two mitochondrial enzymes function in ketolysis whereas a cytosolic enzyme is implicated in cytosolic cholesterol biosynthesis. Cytosolic acetyl-CoA acetyltransferase tetramer (ACAT2 tetramer) (Song et al. 1994) catalyses the condensation of two acetyl-CoA (Ac-CoA) molecules to form acetoacetyl-CoA (ACA-CoA). This is the first step in the biosynthesis of cholesterol (Fukao et al. 1997).