Hormonally Sensitive Esterase Activity in the Mouse Uterus Results from Uptake of Plasma Esterase*

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Abstract
Mouse uterine homogenates contain an estrogen-sensitive serine esterase (hydrolase II). In immature animals, hydrolase II levels increase rapidly after the administration of estradiol. Stimulation of de novo synthesis in the uterus was not demonstrated. It was shown that hydrolase II activity in the uterus results from uptake of an esterase from the blood. The purification of this protein from mouse plasma is described, and some of its properties are discussed. It appears to be similar, if not identical to, a sexually dimorphic plasma esterase called albumin esterase or esterase 1. Consistent with this, hydrolysis of estradiol valerate and .beta.-alanine nitrophenyl ester, by either uterine homogenates or purified esterase 1, was blocked by heating or by incubation with diisopropyl flurophosphate or antibody to esterase 1. Levels of the plasma esterase (esterase 1) were 50% higher in adult female mice than in adult males. Levels in juvenile males were in between those in the adult males and females. No significant changes in esterase 1 plasma levels were detected in any group after 4 days of treatment with either testosterone or estradiol. Like the uptake of other plasma proteins, estrogen-stimulated uterine uptake of the plasma esterase was inhibited by prednisolone, but not by puromycin. Using immunoprecipitation of [35S]methionine-labeled esterase 1 prepared in a cell-free translation system, mRNA specific for esterase 1 was found in mouse liver, but not in mouse uterus. Although the natural substrate for esterase 1 (orhydrolase II) is not known, both the purified enzyme and uterine homogenates were able to hydrolyze the valerate ester of estradiol, but not the stearate ester. Estradiol esters are not necessarily the natural substrates of esterase 1, as only the long chain fatty esters of estradiol are reported to occur in vivo.