Hydrolysis of higher fatty acid esters of p-Nitrophenol by rat liver and kidney lysosomes

Abstract

Esterases, acting on higher fatty acid esters of p-nitrophenol, are shown to be concentrated in the lysosomes of rat liver and kidney by the amount of enzyme sedimented with light mitochondria, by the purification of lysosomes, and by the preparation of Triton WR 1339-filled liver lysosomes. Most of the esterase of liver lysosomes is associated with the lysosomal membrane, whereas a major portion of the kidney lysosomal esterase can be solubilized by freezing and thawing. The pH optimum of the lysosomal esterase of both tissues is between 3.6 and 4. The K m of liver lysosomal esterase for p-nitrophenyl myristate is 0.001 m. The lysosomal esterase is activated by Triton X-100, inhibited by citrate, phthalate, NaCl, EDTA, protamine sulfate, Hg ++, iodoacetate, NaF, deoxycholate, and taurocholate. The esterase is unaffected by 10 −4 m DFP, bovine serum albumin, Triton WR 1339, and most divalent cations. The microsomal esterase of both tissues is powerfully inhibited by 10 −4 m DFP. The relative rates of hydrolysis of p-nitrophenyl esters containing from 8 to 18 carbon atoms in the fatty acid were determined. The lysosomal esterases are least active on p-nitrophenyl caprylate and more active on higher fatty acid esters. The microsomal esterase is most active on p-nitrophenyl caprylate and has very little activity on higher fatty acid esters. The properties of lysosomal acid esterase and acid lipase are discussed.