Purification and characterization of esterase 1F, the albumin esterase of the house mouse (Mus musculus)

Metabolism of KO143, an ABCG2 inhibitor

The ATP-binding cassette sub-family G member 2 (ABCG2) plays an important role in modulating drug disposition and endobiotic homeostasis. KO143 is a potent and relatively selective ABCG2 inhibitor. We found that the metabolic stability of KO143 was very poor in human liver microsomes (HLM). Our further studies illustrated that the tert-butyl ester group in KO143 can be rapidly hydrolyzed and removed by carboxylesterase 1. This metabolic pathway was confirmed as a major pathway of KO143 metabolism in both HLM and mice. K1 is an analog of KO143 without the ester group. We found that the metabolic stability of K1 was significantly improved in HLM when compared to KO143. These data suggest that the ester group in KO143 is the major cause of the poor metabolic stability of KO143. The data from this study can be used to guide the development of KO143 analogs with better metabolic properties.

Purification of a chymotrypsin-like enzyme present on adult Schistosoma mansoni worms from infected mice and its characterization as a host carboxylesterase

A serine protease-like enzyme found in detergent extracts of Schistosoma mansoni adult worms perfused from infected mice has been purified from mouse blood and further characterized. The enzyme is approximately 85 kDa and hydrolyses N-acetyl-DL-phenylalanine β-naphthyl–ester, a chromogenic substrate for chymotrypsin-like enzymes. The enzyme from S. mansoni worms appears to be antigenically and enzymatically similar to a molecule that is present in normal mouse blood and so is seemingly host-derived. The enzyme was partially purified by depleting normal mouse serum of albumin using sodium chloride and cold ethanol, followed by repeated rounds of purification by one-dimensional sodium dodecyl sulphate polyacrylamide gel electrophoresis. The purified material was subjected to tandem mass spectrometry and its derived peptides found to belong to mouse carboxylesterase 1C. Its ability to hydrolyse α- or β-naphthyl acetates, which are general esterase substrates, has been confirmed. A similar carboxylesterase was purified and characterized from rat blood. Additional evidence to support identification of the enzyme as a carboxylesterase has been provided. Possible roles of the enzyme in the mouse host–parasite relationship could be to ease the passage of worms through the host's blood vessels and/or in immune evasion.

Production of ES1 plasma carboxylesterase knockout mice for toxicity studies

The LD(50) for soman is 10-20-fold higher for a mouse than a human. The difference in susceptibility is attributed to the presence of carboxylesterase in mouse but not in human plasma. Our goal was to make a mouse lacking plasma carboxylesterase. We used homologous recombination to inactivate the carboxylesterase ES1 gene on mouse chromosome 8 by deleting exon 5 and by introducing a frame shift for amino acids translated from exons 6 to 13. ES1-/- mice have no detectable carboxylesterase activity in plasma but have normal carboxylesterase activity in tissues. Homozygous ES1-/- mice and wild-type littermates were tested for response to a nerve agent model compound (soman coumarin) at 3 mg/kg sc. This dose intoxicated both genotypes but was lethal only to ES1-/- mice. This demonstrated that plasma carboxylesterase protects against a relatively high toxicity organophosphorus compound. The ES1-/- mouse should be an appropriate model for testing highly toxic nerve agents and for evaluating protection strategies against the toxicity of nerve agents.

N-[(18)F]Fluoroethylpiperidinyl, N-[(18)F]fluoroethylpiperidinemethyl and N-[(18)F]fluoroethylpyrrolidinyl esters as radiotracers for acetylcholinesterase

A series of N-fluoroethylpiperidinyl (1), N-fluoroethylpiperidinemethyl (2) and N-fluoroethylpyrrolidinyl (3) esters were synthesized and examined as new (18)F-labeled radiotracers for measuring brain cholinesterase activity. The fluoroethyl group, instead of methyl group, results in slower in vitro enzymatic cleavage rates and higher selectivity for AChE. Based on metabolism in mouse blood and PET time-activity curves in rats, two radiotracers were identified as potential candidates for further in vivo evaluation in higher species.

Esterase-1: developmental expression in the mouse and distribution of related proteins in other species

Esterase 1 (Es-1) is a sexually dimorphic 65-kDa glycoprotein present in plasma and other murine tissues able to hydrolyze a variety of esters including fatty acid esters of estradiol. Like most other carboxylesterases, its function is unknown. To gain insight into the function of Es-1 and by analogy other carboxylesterases, we have examined the developmental regulation of Es-1 in the mouse and have looked for the presence of related proteins in the plasma of other species. Northern blot analysis of total RNA from the livers of mice of various ages using a 32P-labeled 470-bp Es-1 cDNA probe showed clear postpartum induction with no detectable Es-1 mRNA in fetal liver. Similarly, immunoblotting after sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an affinity-purified rabbit antibody to Es-1 showed no cross-reacting proteins in the plasma until after birth. Northern blot analysis of total RNA from a variety of adult mouse tissues showed the presence of substantial levels of Es-1 mRNA only in liver with lower levels in kidney, testes, and ovaries. Liver mRNA and plasma protein levels rose in parallel attaining full adult levels between 15 and 20 days of age. When plasma proteins were electrophoresed on 7% polyacrylamide gels under nondenaturing conditions, the antibody to Es-1 recognized a low mobility protein in mouse, rat, human, baboon, guinea pig, bovine, horse, and canine but not in chicken plasma. Consistent with the immunoblotting results, the Es-1 cDNA probe hybridized to restriction fragments from human, monkey, rat, and rabbit as well as mouse genomic DNA but not from chicken DNA indicating conservation of the esterase (or esterase-like) gene in mammalian species. The low mobility antigens in mouse and human plasma appeared also to cross-react with antibodies to human thyroglobulin, although antibodies to human thyroglobulin did not appear to recognize Es-1 under these conditions.

Characterization and functional expression of a cDNA encoding egasyn (esterase-22): the endoplasmic reticulum-targeting protein of beta-glucuronidase

Egasyn (esterase-22), a member of the nonspecific carboxylesterase multigene family (E.C. 3.1.1.1), is the endoplasmic reticulum (ER)-targeting protein of beta-glucuronidase. We utilized the polymerase chain reaction (PCR) in the eventual isolation of murine egasyn cDNAs. PCR primers were based upon: (1) partial amino acid sequences derived from egasyn peptides and (2) a conserved active site region shared by carboxylesterases. The amino acid sequence deduced from the PCR product matched that obtained from egasyn protein. This product was utilized as a probe to screen a cDNA library. Two cDNAs whose composite sequence encoded an open reading frame of 562 amino acids were isolated. A message size of 1700-2000 bp was revealed by RNA blot hybridization analysis. S1 nuclease protection analyses detected mRNA in liver, kidney, lung, and submandibular gland, but not in spleen, brain, and testes. Genetic mapping confirmed the location of an egasyn cDNA fragment in cluster 1 of the esterase region on chromosome 8. Transfection of COS cells with the 2022-bp cDNA resulted in the expression of esterase activity, which comigrated on native gels with liver esterase-22. The features of the deduced amino acid sequence of the egasyn cDNA are compared with previously characterized carboxylesterases and with other lumenal ER proteins.

Characterization of a murine cDNA encoding a member of the carboxylesterase multigene family

We have characterized a mRNA sequence containing the entire coding region of a mouse carboxylesterase (EC 3.1.1.1). pEs-N, an 1840-bp composite of five overlapping cDNA clones, contains an open reading frame of 554 amino acids that display a high degree of similarity with rat and rabbit carboxylesterases. Genetic mapping studies place this carboxylesterase in cluster 1 of the esterase region on chromosome 8. Results of blot hybridization analysis of genomic DNA probed with a pEs-N cDNA under both low and high stringency conditions suggest membership in a carboxylesterase multigene family, as would be expected for a nonspecific carboxylesterase. A message size of 1850-1900 nucleotides was revealed by RNA blot hybridization analysis. S1 nuclease protection analyses with a probe representing a segment of pEs-N detected message in liver, kidney, and lung, but not in spleen, brain, testes, and submandibular gland, with higher levels in female than in male kidney. Additional S1 nuclease-protected mRNA species were found, suggesting the expression of distinct members of a multigene family. In vitro translation of a full-size transcript of pEs-N resulted in a product of 51.5 kDa. Upon the addition of microsomes, this product was processed into a protein of 60.4 kDa, which is within the size range of monomeric units of mouse carboxylesterases.

Micro two-dimensional gel electrophoresis of serum and testis esterases from different strains of mice

Two-dimensional electrophoresis with time-dependent polyacrylamide gradient gel electrophoresis (PAGGE) in the second dimension was applied to the separation of native molecular forms of esterases from serum and testis of four strains of mice (C57BL/6J, Swiss OF1, F1 hybrid derived from these two populations and Tfm). In Phast System, a modified pH 3-9 gradient, a linear 8-25% gel gradient and a migration time corresponding to 300 Vh, were found to provide the best conditions for esterase analysis. About 70 esterase-active fractions could be separated with good reproducibility. The variants were characterized by their pI (3.9-7.35), their relative mobility and the visual estimation of their susceptibility towards neuraminidase and different esterase inhibitors. In the two tissues, the distribution of the esterase variants corresponded to a 50-500 kDa molecular mass range of calibration proteins, but most of the serum and testis-specific isoforms were confined to the 59-72 kDa range. All serum variants contained a terminal N-acetylneuraminic acid residue, whereas only the testicular esterases in common with those in serum appeared sensitive to neuraminidase. Cholinesterases with a low relative mobility and carboxylesterases with a high relative mobility were detected in serum, while carboxylesterases accounted for the greatest part in the testis which also contained cholinesterases and acetylesterases. Minor interspecies differences were found between C57BL/6J and Swiss OF1 esterases. The expression of two variants which differed between these two species seemed intermediate for the hybrid originating from these two populations. Two new spots were detected in the two-dimensional map of esterases from the strain bearing the Tfm mutation.

Physical and chemical characterization of a horse serum carboxylesterase

The serine carboxylesterase from horse serum was characterized by amino acid composition, peptide mapping, molecular and subunit weights, and sequencing of the amino acids around the essential serine residue at the active site. A protocol was developed for using reversed-phase high-performance liquid chromatography as the final step to obtain homogeneous preparations of horse serum carboxylesterase. Amounts sufficient for determining the amino acid composition and for peptide maps were obtained from a partially purified starting material which contained approximately 55% carboxylesterase. The amino acid composition, like the subunit weight (70,800 +/- 1400), was similar to the corresponding values reported for other serine carboxylesterases. However, the amino acid sequence of the tryptic digest fragment containing the essential nucleophilic seryl residue differed significantly from the corresponding sequences of other mammalian serine carboxylesterases.

cDNA cloning of esterase 1, the major esterase activity in mouse plasma

We report here the cloning of a partial cDNA for Esterase 1, the major esterase activity in mouse plasma. A 470 base pair insert was isolated from a lambda gt11 cDNA library constructed from mouse liver poly A+ RNA, and identified by hybrid selected translation. We show that the sexual dimorphism displayed in the plasma levels of this protein is caused by a difference at the level of transcription. In addition, RFLP data using mouse recombinant inbred strains mapped this clone at the Es-1 locus on mouse chromosome 8.

Lymph esterases of the house mouse (Mus musculus)--II. The role of esterase-2 in fat resorption

1. Intralipid infusion into the duodenum of Mus musculus was accompanied by changes in lymph and serum concentrations of two esterase isozymes, ES-1 and ES-2. Whereas ES-1 levels declined in both lymph and serum, ES-2 levels increased 5-fold in lymph within 120 min, and fell to a plateau 3- to 4-fold the fasting level; serum levels of ES-2 increased continually. 2. The changes in lymph ES-2 concentrations were paralleled by lymph triglyceride concentration during Intralipid infusion. Genetically determined differences in the concentration of two allozymes, ES-2B and ES-2D, were reflected in differences in lymph triglyceride levels. The lymph triglyceride concentration was strongly correlated with approximately the cube root of the lymph ES-2 concentration for both allozymes. 3. The source of lymph ES-2 during fat resorption was probably an intracellular jejunal pool; serum ES-2 also re-entered the lymph but this fraction was not influenced by fat resorption. 4. Purified chylomicrons possessed no esterase activity; however, it was postulated that ES-2 plays an essential role in fat resorption and is extruded with the primary chylomicrons from the enterocyte.

Lymph esterases of the house mouse (Mus musculus)--I. Identification and possible origins of abdominal lymph esterases

1. Abdominal lymph was obtained from Mus musculus by cannulation of the thoracic duct: lymph esterases were identified by polyacrylamide gel electrophoresis. Seven known esterases (ES-1, ES-2, ES-5, ES-27, SE-I, SE-II and SE-III) and a newly described activity (SE-IV) were demonstrated, all of which were also present in serum. 2. Electrophoretic staining intensities indicated that the lymph esterases were less concentrated than the corresponding activities in serum, with the single exception of ES-2. This finding was supported by quantitative immunoelectrophoresis of ES-1 and ES-2 (two allozymes each). 3. The jejunum appeared to be the origin of lymph ES-2 by a comparison of organ distribution of the allozymes ES-2B and ES-2D and by monitoring the re-appearance of ES-2 in several organs, serum and lymph after total inhibition in vivo by bis-p-nitrophenyl phosphate.

Esterases in inbred strains of mice with differential cholesterolemic responses to a high-cholesterol diet

Specific esterase isoenzyme patterns in plasma may be associated with responsiveness of serum cholesterol to dietary cholesterol. In rabbits and rats the presence and absence of a high-mobility, anodal esterase band on electrophoresis have been shown to be associated with hypo- and hyperresponsiveness, respectively. We fed for 28 days male mice of 7 inbred strains either a low-cholesterol, commercial diet or a diet containing 2% (w/w) cholesterol, 0.5% cholic acid and 5% olive oil. Feeding the high-cholesterol diet revealed marked inter-strain differences in the responses of plasma and liver cholesterol; the increases ranged from 21 to 129% and from 10 to 80-fold, respectively. There was no association between esterase isoenzyme patterns in plasma and the sensitivity to the high-cholesterol diet. The mean baseline plasma total esterase activity tended to be positively associated with the absolute response of plasma cholesterol to the high-cholesterol diet (r = 0.56; n = 7), but the positive relationship between the baseline concentration of the ES-1 component in plasma and the cholesterolemic response was stronger (r = 0.84; n = 7; P less than 0.05). The high-cholesterol diet caused a significant increase in plasma total esterase activities in 6 out of the 7 strains. Evidence is presented that the increase in plasma total esterase activity, which was associated with an increase in the activity and concentration of the so-called ES-2 isoenzyme, is the result of an enhanced release of esterases from the intestine, rather than from the liver. A significant, positive correlation was found between the baseline intestinal esterase activity and the cholesterolemic response after cholesterol feeding (r = 0.83; n = 7; P less than 0.05).

Electrophoretic characterization of mouse epididymal esterases in inbred lines and in a natural population

Esterase isozymes were studied in mouse epididymis of two inbred strains (C57BL, DBA/2) and in a natural population (Swiss OF1), by using vertical polyacrylamide gel electrophoresis and staining with alpha or beta-naphthyl acetate as a substrate. Eighteen (C57BL), 17 (DBA/2) or 16 (Swiss OF1) epididymal isozymes were separated; four were common to the testis, and five to both the testis and the serum. The use of different inhibitors showed that carboxylesterase activities account for the greater part of the total epididymis non-specific esterase activity. This comparative study revealed minor interspecies variations since only two isozymes were not expressed in the same manner in the three populations examined. Among the nine isozymes which appeared solely in the epididymis, the profiles varied between tissues and fluids as well as between the proximal part in which sperm maturation occurs and the distal part where sperm storage takes place. The variations proceeded from the relative activity of isozymes and the presence or absence of some of them; two characterized the proximal part and one the distal part in the three species. By comparing testis and epididymal tissues and fluids, it is suggested that the isozymes found in epididymal fluids originated from the testis, the epididymal epithelium or both. In addition to this epididymal secretory function, the lack in the fluid of the distal part of one isozyme identified in the testis, and two in the proximal part may also provide evidence for its reabsorptive function.

Nonspecific esterases of mammalian testis. Comparative studies on the mouse (Mus musculus) and rat (rattus norvegicus)

Ten different nonspecific esterases in both mouse (Mus musculus) and rat (Rattus norvegicus) testis were identified following the analysis of electrophoretic patterns using genetic, developmental, and biochemical criteria. None of the enzymes were unique to testis, although the pattern of activity was testis specific. The enzymes comprised, in each species, six carboxylesterases (EC 3.1.1.1), one arylesterase (EC 3.1.1.2), one acetylesterase (EC 3.1.1.6), and two butyrylesterases (tentative designation). Cholinesterase (EC 3.1.1.8) was not detected. Individual homology relationships were recognized between the two species for all of these activities, except three of the carboxylesterases; however, these were coded for by homologous gene clusters. Similarities between the two species extended to the developmental course of expression and the modulation of the pattern of activity by the testicular feminization (Tfm) mutation. We describe the effects of the sex reversal (Sxr) mutation in the mouse, as well as the distribution of individual activities between Leydig cells and seminiferous tubules. The results of earlier histochemical studies are interpreted in the light of the present investigation. The correspondence between mouse- and rat-testis esterases suggests that the results could serve as a basis for mammalian testis esterase systems in general.

Identification and development of a genetically closely-linked carboxylesterase family of the mouse liver

Six carboxylesterase isozymes (viz. ES-1, ES-6, ES-9, ES-20, ES-22 and ES-24), governed by esterase gene cluster 1 on chromosome 8 of the house mouse, were identified electrophoretically in liver supernatants using their biochemical, genetic and developmental characteristics. ES-1 and ES-20 were expressed as liver-specific forms. The peri- and postnatal development of the six isozymes indicated that they were individually regulated at the genetic level, although the isozymes were regulated as a group when compared to genetically unrelated esterases. The concept of evolutionary divergence following repeated gene duplication of an ancestral esterase structural gene was extended to cover divergence of the temporal (regulatory) genes associated with the multigene family. Allelic variation of the temporal genes was more limited than that of the corresponding structural genes.

Purification and characterization of esterase 6A, a trimeric esterase of the house mouse (Mus musculus)

Esterase 6A was isolated from mouse lung and purified 440-fold by ion-exchange chromatography, inverse ammonium sulphate gradient solubilization, gel filtration and isoelectric focusing. The resultant product was apparently homogenous by the criteria of polyacrylamide gel electrophoresis and immunodiffusion, and consisted of the electrophoretic form 6A3. A single species of subunit was present on sodium dodecyl sulphate gel electrophoresis. The molecular weight of the native protein was found to be about 178,000 with a subunit molecular weight of about 60,000. The equivalent weight obtained by active-site titration with diethyl-p-nitrophenyl phosphate was approximately 178,000 g/mol, indicating a functional asymmetry in the trimer. The enzyme was shown to have a high affinity for 4-nitrophenyl hexanoate (Michaelis constant Km = 4.4 mumol/l) with a relatively low catalytic efficiency (catalytic constant kcat = 12 s-1). Esterase 6A was immunologically related to esterase 1 and esterase 9, with which it is genetically closely linked. Further properties of the three esterases were compared.

Dynamics of non-specific esterase during fat resorption in the jejunum of the house mouse, Mus musculus

The dynamics of non-specific esterase in the upper duodenum of the house mouse was studied electron microscopically at various intervals following a fat meal. Enterocytic esterase became associated with lipid droplets during fat resorption and formation of primary chylomicrons. Esterase activity remained associated with the primary chylomicrons throughout the process of extrusion into the extracellular space at the lateral interdigitations, and during subsequent transport into the lymph vessels. It is suggested that certain isozymes of non-specific esterase participate in lipid transport.

Interstrain variation of esterase-22, a new isozyme of the house mouse

1. A new liver esterase in the house mouse, ES-22, is described, using different staining methods after dose electrophoretic separation on polyacrylamide gels. 2. Five different phenotypes, ES-22A to ES-22E, could be distinguished in various mouse strains. ES-22 is genetically closely linked to ES-6, ES-9 and ES-20 on chromosome 8, but its distribution among different strains appears to be independent from these isozymes. 3. ES-22 is clearly different from other chromosome 8-controlled esterases, with respect to its organ expression and its catalytic properties. 4. A gene locus Es-22 with five alleles is suggested. 5. It is proposed that the genes coding for the carboxylesterase isozyme system on chromosome 8 constitute a multigene family as defined by Hood et al. (1975).

Esterase-16 (es-16): characterization, polymorphism, and linkage to chromosome 3 of a kidney esterase locus of the house mouse

A polymorphism for an isozyme of a presumed arylesterase, esterase-16 (EC 3.1.1.2), has been detected in kidney, heart, and spleen of the house mouse, Mus musculus, by means of isoelectric focusing and by disc electrophoresis. Three phenotypes can be distinquished: the ES-16A phenotype (IEP 5.9) was found in C57BL/10Sn and many other laboratory inbred strains; the ES-16B phenotype (IEP 6.1) was found in M. m. molossinus; and the ES-16C phenotype (IEP 5.9; very weak activity) was found in Peru-Coppock. Esterase-16 is strongly inhibited by 10(-3) M p-chloromercuribenzoate, but not by 2. 10(-4) M bis-p-nitrophenyl phosphate or by 10(-3) M Diamox. It stains well with indoxyl acetate and other indigogenic substrates but only weakly with alpha-naphthyl acetate. Esterase-16 is completely insoluble in water. It is apparently governed by a structural gene locus, Es-16, with three alleles, Es-16a, Es-16b, and ES-16c, respectively. Es-16 is closely linked to Car-1 and Car-2 on chromosome 3 Typing of 94 animals of the backcross (C57BL/10Sn x M. m. mol.) F1 x M. m. mol. revealed a recombination frequency of 8.51 /+- 2.9%.