An acyl-CoA hydrolase, referred to as hBACH, was purified from human brain cytosol. The enzyme had a molecular mass of 100 kDa and 43-kDa subunits, and was highly active with long-chain acyl-CoAs, e.g. a maximal velocity of 295 micromol/min/mg and K(m) of 6.4 microM for palmitoyl-CoA. Acyl-CoAs with carbon chain lengths of C(8-18) were also good substrates. In human brain cytosol, 85% of palmitoyl-CoA hydrolase activity was titrated by an anti-BACH antibody, which accounted for over 75% of the enzyme activity found in the brain tissue. The cDNA isolated for hBACH, when expressed in Escherichia coli, directed the expression of palmitoyl-CoA hydrolase activity and a 44-kDa protein immunoreactive to the anti-BACH antibody, which in turn neutralized the hydrolase activity. The hBACH cDNA encoded a 338-amino acid sequence which was 95% identical to that of a rat homolog. The hBACH gene spanned about 130 kb and comprised 9 exons, and was mapped to 1p36.2 on the cytogenetic ideogram. These findings indicate that the long-chain acyl-CoA hydrolase present in the brain is well conserved between man and the rat, suggesting a conserved role for this enzyme in the mammalian brain, and enabling genetic studies on the functional analysis of acyl-CoA hydrolase.

No abstract

Acyl-CoA hydrolases cleave acyl-CoA thioesters to free fatty acids and coenzyme A. The potency of these enzymes may serve to modulate cellular levels of acyl-CoAs to affect various cellular functions, including lipid metabolism. In this study, we investigated the tissue distribution of this multigene family of enzymes, focusing on cytosolic (CTE-I) and mitochondrial acyl-CoA thioesterases (MTE-I) in adult rats, using an anti-CTE-I antibody which recognizes both the isoforms. Western blotting detected them mainly in organs closely related to fatty acid oxidation, of which kidney contained the highest levels of both enzymes. Immunohistochemistry localized the enzymes primarily in the proximal tubules, where a large energy demand is expected and fatty acids represent a major fuel, correlating well with the intrarenal distribution of peroxisomal beta-oxidation. In situ hybridization suggested colocalization of CTE-I and MTE-I in the kidney. The immunoreactivity was also found in various epithelial tissues in the body, including Harderian gland and sebaceous gland. These results demonstrated the distribution of CTE-I and MTE-I in a wide variety of rat tissues, primarily characterized by an epithelial localization, being consistent with their involvement in fatty acid metabolism.