Induction of a microsomal butyrylesterase in rat liver by phenobarbital treatment

A carboxylesterase (carboxylic-ester hydrolase, EC 3.1.1.1) was induced in the liver of rats after repeated administration of phenobarbital. This enzyme migrated most rapidly towards the anode among Triton X-100-solubilized liver esterases by electrophoresis on the cellulose acetate membrane and it was tentatively designated as L-I. L-I increased in the microsomal fraction and was mainly concentrated in the fraction of smooth endoplasmic reticulum that proliferated after phenobarbital treatment. L-I- was separated from other liver esterases and purified about 800-fold. The purified L-I was homogeneous as judged by polyacrylamide gel electrophoresis and exhibited a molecular weight of about 55 000 as determined by gel filtration. L-I split the 1-naphthyl ester of butyric acid faster than esters of acetic, propionic or valeric acids; it therefore seemed to be a butyrylesterase.