Very long chain and long chain acyl-CoA thioesterases in rat liver mitochondria. Identification, purification, characterization, and induction by peroxisome proliferators.

We have previously reported that long chain acyl-CoA thioesterase activity was induced about 10-fold in rat liver mitochondria, when treating rats with the peroxisome proliferator di(2-ethylhexyl)phthalate (Wilcke M., and Alexson S. E. H (1994) Eur. J. Biochem. 222, 803-811). Here we have characterized two enzymes which are responsible for the majority of long chain acyl-CoA thioesterase activity in mitochondria from animals treated with peroxisome proliferators. A 40-kDa enzyme was purified and characterized as a very long chain acyl-CoA thioesterase (MTE-I). The second enzyme was partially purified and characterized as a long chain acyl-CoA thioesterase (MTE-II). MTE-I was inhibited by p-chloromercuribenzoic acid, which implicates the importance of a cysteine residue in, or close, to the active site. Antibodies against MTE-I demonstrated the presence of immunologically related acyl-CoA thioesterases in peroxisomes and cytosol. High expression of MTE-I was found in liver from peroxisome proliferator treated rats and in heart and brown fat from control and induced rats. Comparison of physical and catalytical characteristics of the enzymes studied here and previously purified acyl-CoA thioesterases suggest that MTE-I and MTE-II are novel enzymes.