LONG-CHAIN ACYL-COA HYDROLASE FROM RAT-BRAIN CYTOSOL - PURIFICATION, CHARACTERIZATION, AND IMMUNOHISTOCHEMICAL LOCALIZATION

Long-chain acyl-CoA hydrolase (EC 3.1.2.2), which is found primarily i n the brain in rats, catalyzes the hydrolysis of fatty acyl-CoA thioes ters. We purified this enzyme, referred to as ACH, from the rat brain cytosol. The molecular masses of the native enzyme and the subunit wer e estimated to be 104 and 36 kDa, respectively. The enzyme showed high activity with long-chain acyl-CoAs, e.g., with maximal velocity of 26 2 mu mol/min/mg and K-m of 5.7 mu M for palmitoyl CoA, but acyl-CoAs w ith carbon chain lengths of C-8-18 were also good substrates. The enzy me was refractory to the inhibitory effect of diisopropyl fluorophosph ate and phenylmethylsulfonyl fluoride, but sensitive to p-chloromercur ibenzoate. In the rat brain cytosol, about 90% of palmitoyl-CoA hydrol ase activity was titrated by anti-ACH antibody, which accounted for ov er 70% of the enzyme activity found in the brain tissue. Immunoblots o f the cytosol prepared from rat brain regional blocks indicated the br oad distribution of ACH over the brain, with a relatively high level i n the pens and medulla. Immunohistochemically, ACH was localized to ne urons. In addition to various nuclei, some neuronal cells, such as mit ral cells in the olfactory bulb, pyramidal cells in the cerebral corte x, and Purkinje cells in the cerebellum, were also immunostained with anti-ACH antibody. Brain cytosols prepared from ten mammalian species including human contained a single polypeptide reactive to anti-ACH an tibody with molecular masses of 34-36 kDa, together with high activiti es of palmitoyl-CoA hydrolase. These findings suggest the physiologica l significance of ACH in the brain, although its precise role remains to be determined. (C) 1996 Academic Press, Inc.