Thioesterase with a preference for ring-hydroxylated phenylacetyl-CoA esters. Hydrolyzes 3,4-dihydroxyphenylacetyl-CoA, 3-hydroxyphenylacetyl-CoA and 4-hydroxyphenylacetyl-CoA. Inactive towards 4-hydroxybenzoyl-CoA and 4-hydroxyphenacyl-CoA. Optimum pH is 7.5-9. Aromatic compound metabolism; phenylacetate degradation. Homotetramer. Activated by cAMP receptor protein (CRP), integration host factor (IHF) and by phenylacetyl-coenzyme A (PA-CoA) that prevents PaaX from binding its target sequences. Inhibited by PaaX. Belongs to the thioesterase PaaI family.