Immunochemical studies on a phenobarbital-inducible esterase in rat liver microsomes

Detergent extracts of liver microsomes from drug-treated rats were analyzed semiquantitatively in crossed immunoelectrophoresis in combination with a zymogram technique for nonspecific esterase activity. One esterase-active antigen was quantitatively induced by phenobarbital as demonstrated with both antimicrosomal antiserum and a monospecific antiserum prepared against this antigen. No similar inducation of this or any other esterase-active antigen was detected after 3-methylcholanthrene treatment. With the monospecific antiserum, the antigen was also detected in other organs, capable of carrying out hydroxylation reactions, such as lung and kidney. It was, however, not induced by phenobarbital in these organs. Quantitative enzyme assays with acetanilide as substrate indicated that the phenobarbital-inducible esterase could also function as an amidase. Furthermore, from absorption studies, it was concluded that this antigen is located on the cytoplasmic side of the microsomal vesicles. Crossed immunoelectrofocusing experiments revealed that this esterase-active antigen consists of five subcomponents with different charge properties.