Purification and characterization of various esterases from rat liver.

The major rat liver microsomal esterases acting on o-nitrophenylacetate with isoelectric points 5.0, 5.5, 6.1 and 6.4 were resolved by isoelectric focusing. Molecular weights were determined by sedimentation analysis in isokinetic gradients of sucrose and, after purification, in sodium dodecyl sulphate/polyacrylamide gel electrophoresis. Their subunit molecular weights were between 57 000 and 60 000. They behaved as monomers except the pI-6.1 enzyme which behaved as a trimer. Esterases of pI 5.0, pI 6.1 and pI 6.4 behaved like glycoproteins of the polymannose type in the presence of 125I-labelled concanavalin A. Preparations of the pI-5.0 enzyme contained two esterases of highly homologous structure. Antibodies directed against this preparation did not inhibit but precipitated pI-5.0 esterase activity quantitatively. They did not react with the pI-6.1 and pI-6.4 esterases but precipitated several nonimmunologically related esterases. Two of these enzymes were inducible by phenobarbital. Total activity was very low in 3-day-old animals. Individual esterase activities rose at different rates during development; the enzyme focusing near pI 5.0 was about three times more active in adult females than in males. All microsomal esterases are located on the luminal side of the endoplasmic reticulum.