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any of the enzymes of the hydrolase class that catalyze the cleavage of the ester bond in organic compounds. In the broad sense of the word, esterases include lipases, phosphatases, and sulfatases, in addition to esterases proper, among which are many specific enzymes, such as cholinesterase, chlorophyllase, tannase, and pectinase. Esterases are found in humans, animals, higher plants, and microorganisms. In humans and animals, they are found in pancreatic juice (pancreatic lipase, or steapsin), blood, and milk; they are also found in the liver, the intestinal walls, and various tissues.