Immunochemical characterization of esterase active antigens in rat liver microsomes

Ten distinct immunoprecipitates with esterase activity were identified in the reaction between rat liver microsomes and rabbit anti-rat liver microsomal antisera in crossed immunoelectrophoresis. These esterases were further characterized by the use of inhibitors, different substrates, hormone induction experiments and cross-reactivity studies with microsomes from other organs. Two of the esterase active antigens were found to be present in 2–3-fold higher concentrations in microsomes from female than male liver. Administration of the female sex hormone estradiol to male rats caused an induction of these esterases to the female level. The microsomal esterases showed a preference to hydrolyze substrates with short fatty-acid chains. Only one esterase could attack acetyl- and butyrylthiocholine. It was also inhibited by 10−3M eserine and was thus considered to be a cholinesterase. All esterases except one were inhibited by 10−3M DFP. In cross-reactivity experiments it was shown that this DFP insensitive esterase was also present in lung and testes microsomes. Kidney microsomes had two other esterases in common with liver, while microsomes from intestine, ovaries and heart gave one weak and diffuse precipitate, not further characterized, with the rabbit anti-rat liver microsomal antiserum.