Abstract
An extramitochondrial acetyl-CoA hydrolase [EC 3. 1. 2. 1] in the rat liver, which is stimulated by ATP and inhibited by ADP, is known to be extremely cold-labile. During subcellular fractionations at low temperatures (2-4°C), most of the enzyme activity was lost; however, most could be recovered by rewarming at 37°C in the presence of a high concentration of potassium phosphate. This enabled us to measure the activities of cold-treated samples. The majority of the ATP-stimulated and ADP-inhibited acetyl-CoA hydrolase activity in rat livers was detected in the cytosolic fraction and small amounts were detected in the peroxisomal fraction. The activity of peroxisomal ATP-stimulated acetyl-CoA hydrolase was not noticeably increased after clofibrate-treatment. However, the cytosolic activity greatly increased after clofibrate treatment. The activity in the isolated peroxisomal fraction per g of liver was about 5% of that in the cytosolic fraction of liver from the control and about 2% in that from clofibrate-treated rats. Besides having similar nucleotide (ATP and ADP) sensitivity and cold lability, the enzyme protein in the peroxisomal fraction migrated to the same position as the cytosolic acetyl-CoA hydrolase based on Western blot analysis with antibody against purified acetyl-CoA hydrolase from rat liver cytosol. These results suggest that the peroxisomal enzyme and cytosolic enzyme may be the same entity.
