MonCII from the monensin biosynthetic gene cluster in Streptomyces cinnamonensis, which was previously thought to be an epoxide hydrolase, is a novel thioesterase. It hydrolyse several thioester substrates, including an N-acetylcysteamine thioester derivative of monensin A (strci-MONAIX and strci-MONAX are thioesterases typeII)