Carboxymethylenebutenolidase homolog（CMBL) is a cysteine hydrolase of the dienelactone hydrolase family which is highly expressed in the liver cytosol. CMBL is the human homolog of Pseudomonas dienelactone hydrolase， which is a protein that participates in the bacterial halocatechol degradation pathway. CMBL which preferentially cleaves cyclic esters activates medoxomil-ester prodrugs in which the medoxomil moiety is coupled with an oxygen atom. CMBL is inhibited by PCMB（p-chloromercuribenzoate) and is encoded by a gene which maps to human chromosome 5p15.2. Furthermore， CMBL converts the prodrug olmesartan medoxomil into its pharmacologically active metabolite olmerstatan， which is an angiotensin receptor blocker， in the liver and intestine. CMBL can also activate beta-lactam antibiotics faropenem medoxomil and lenampicillin. CMBL is widely expressed， with the highest levels in the liver， followed by the kidney， small intestine and the colon.
