24] Carboxylesterases from pig and ox liver

Abstract

Publisher Summary This chapter discusses the determination of carboxylesterases from pig and ox liver. Carboxylesterases are remarkably efficient enzymes that catalyze the hydrolysis of a wide range of alkyl and aryl esters of aliphatic and aromatic carboxylic acids. The hydrolysis of anilides (for example, acetanilide, phenacetin, and xylocaine) and of thiol esters (for example, ethyl thiolacetate, and phenyl thiolacetate) is also catalyzed. In addition, carboxylesterases catalyze the transfer of the acyl moiety of substrate molecules to nucleophiles such as alcohols and amines. It has been demonstrated that amino acid esters act as acyl acceptors, and that ox liver carboxylesterase catalyze the synthesis of phenylalanylphenylalanine methyl ester and of the dipeptide itself, starting with phenylalanine methyl ester as substrate. In the course of purification procedure for pig liver carboxylesterase, pig liver carboxylesterase is slowly denatured at pH 5 and below, and therefore exposure of the enzyme to low pH should be brief. In the course of purification procedure for ox liver carboxylesterase, homogenize 1 kg of fresh ox liver mince with 5 liters of redistilled acetone (–30 to –10°) in an explosion-proof Waring blender. Filter the acetone through a large Buchner funnel (24 cm, Whatman No. 542 paper). Wash the filter cake and dry it in exactly the same way that the pig liver powder was treated. Store the thoroughly dried powder (200–250 g) in an air-tight jar at 4 °.