Peptide synthetases are involved in the non-ribosomal synthesis of peptide antibiotics. Next to the operons encoding these enzymes, in almost all cases, are genes that encode proteins that have similarity to the type II fatty acid thioesterases of vertebrates. There are also modules within the peptide synthetases that also share this similarity. With respect to antibiotic production, thioesterases are required for the addition of the last amino acid to the peptide antibiotic, thereby forming a cyclic antibiotic. Thioesterases (non-integrated) have molecular masses of 25-29 kDa.

1: Genetic evidence for a role of thioesterase domains, integrated in or associated with peptide synthetases, in non-ribosomal peptide biosynthesis in Bacillus subtilis. Schneider A, Marahiel MA; Arch Microbiol 1998;169:404-410. PMID:9560421