Multiplicity and Acylation/Deacylation Capability of Liver Microsomal Carboxyl este rase Isozymes in Several Animal Species and Humans

Twenty-five forms of carboxylesterase isozymes were purified to electrophoretic homogeneity from liver microsomes of rats, mouse, hamster, guinea pig, rabbit, beagle dog, pig, cow, cynomolgus monkey, rhesus monkey and humans by the same procedure used, and their physical, enzymological and immunological properties were compared with each others. The substrate specificity and immunological reactivity of liver microsomal carboxylesterase from above animals were also examined for comparison. The twenty-five purified preparations have similar subunit weight (57, 000-64, 000), but their isoelectric point differ widely (4.3-6.5). Anti-rat RH1 IgG was found to possess high cross-reactivity with many isozymes tested by immunoblotting analysis. The amino-terminal amino acid sequences showed a striking homology, except for monkey MK2. However, differential capability of acylation/deacylation of endogenous and xenobiotic compounds by above carboxylesterase isozymes from various mammals and humans. Hepatic microsomal carboxylesterases in mammals play an important role in drug and lipid metabolism in the endoplasmic reticulum, and it is noteworthy that the isozymes from various species examined here showed considerable similarities in physical and immunochemical properties, but not similar in substrate specificity.