Has acyl-CoA thioesterase activity towards medium and long-chain (C14 to C18) fatty acyl-CoA substrates, and probably plays a role in mitochondrial fatty acid metabolism. Plays a role in the apoptotic process, possibly via its regulation of AKT1 activity. According to PubMed:11598301, inhibits AKT1 phosphorylation and activity. According to PubMed:17615157, enhances AKT1 activity by favoring its phosphorylation and translocation to plasma membrane. H2O + hexadecanoyl-CoA = CoA + H(+) + hexadecanoate H2O + octanoyl-CoA = CoA + H(+) + octanoate decanoyl-CoA + H2O = CoA + decanoate + H(+) dodecanoyl-CoA + H2O = CoA + dodecanoate + H(+) H2O + tetradecanoyl-CoA = CoA + H(+) + tetradecanoate (9Z)-octadecenoyl-CoA + H2O = (9Z)-octadecenoate + CoA + H(+) (5Z,8Z,11Z,14Z)-eicosatetraenoyl-CoA + H2O = (5Z,8Z,11Z,14Z)-eicosatetraenoate + CoA + H(+) Homodimer and homotetramer. Interacts with AKT1 in the cytosol. Released from the mitochondria into the cytosol in response to apoptotic stimuli. Expressed predominantly in skeletal muscle, testis, uterus, brain and kidney. Down-regulated in glioblastoma or glioma compared to non-neoplastic brain due to promoter hypermethylation. Phosphorylated. Belongs to the THEM4/THEM5 thioesterase family.