SUBCELLULAR DISTRIBUTION AND SOME PROPERTIES OF ACETYL-COENZYME A HYDROLASE IN THE BRAIN

—The detailed subcellular distribution and some properties of acetyl-CoA hydrolase were studied in the rat brain. The brain homogenate (S₁) hydrolysed acetyl-CoA at a rate of approx 2·3 nmol/min/mg of protein at 37°C. The total activity of acetyl-CoA hydrolase was distributed in the following order: soluble > mitochondrial > microsomal, synaptosomal > myelin fraction. The order of the specific activity of the enzyme was: soluble, microsomal > mitochondrial > synaptosomal > myelin fraction. The synaptic vesicle fraction (D) had relatively high specific activity among the intraterminal particulate fractions, having two or three times higher specific activity than that of the synaptic cytoplasmic membrane fraction (F or G). Attempts to de-occlude acetyl-CoA hydrolase in the particulate fraction showed that only the enzyme activity in the myelin fraction was increased markedly by the treatment with ether or Triton X-100. Lineweaver-Burk plots gave straight lines for each subcellular fraction and apparent K_m values for acetyl-CoA were between 0·1 and 0·2 mM. Neither diisopropyl fluorophosphate nor physostigmine at the concentration of 0·1 mm inhibited the enzyme activity.