The recombinant polyketide synthase thioesterase domains from the pimaricin and 6- deoxyerythronolide B biosynthetic pathways catalyze hydrolysis of a number of simple N- acetylcysteamine thioester derivatives. This study demonstrates that thioesterases are not highly substrate selective in formation of the acyl-enzyme intermediate, in contrast to non- ribosomal peptide synthase thioesterase domains that show very high specificity for ...