MBL(carboxymethylenebutenolidase homolog) is a 245 amino acid cytosolic protein and cysteine hydrolase of the dienelactone hydrolase family that is highly expressed in liver cytosol. CMBL is the human homolog of Pseudomonas dienelactone hydrolase, a protein that participates in the bacterial halocatechol degradation pathway. That is ubiquitously expressed with high expression in liver, colon, kidney and small intestine, where it acts as a bioactivating enzyme for a prodrug type angiotensin II type 1 receptor antagonist known as olmesartan medoxomil. CMBL is inhibited by p-chloromercuribenzoate (PCMB).