Two families of acyl-CoA thioesterases in Arabidopsis

We have identified two families of acyl-CoA thioesterase (ACHs) in Arabidop sis thaliana. One family, consisting of AtACH1 and AtACH2, appears to be, p eroxisomal, as they have type-1 peroxisomal targeting sequences. The other family, consisting of AtACH4 and AtACH5, resides in the endoplasmic reticul um, as shown by green fluorescent protein studies. AtACH2 has been overexpr essed in Escherichia coli and shows high levels of acyl-CoA thioesterase ac tivity against both 16:0-CoA and 18:1-CoA. AtACH5 has also been overexpress ed in E. coli, and shows thioesterase activity as well. ACHs have been char acterized in other many other organisms and in various subcellular location s, but their true physiological role is not yet understood. Indeed, atach5 gene knockout mutants have no observable phenotype.