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Serum cholinesterase (BChE) and carboxylesterase (CbE) activities were investigated in ten species of birds. Multiple forms of serum BChE and CbE were also separated by chromatofocusing. Higher CbE activity and a wider range of CbE and BChE forms were present in the sera of omnivorous/herbivorous birds than carnivores. Omnivores/herbivores studied were the starling, house sparrow, tree sparrow, pigeon, partridge and magpie. Serum CbE activities of these species ranged from 0.46 to 2.93 mumol/min/mL with 2-6 forms separated by chromatofocusing. 0-6 forms of BChE were separated by the same method. The serum CbE activities of the little owl, tawny owl, barn owl and razorbill ranged from 0.19 to 0.58 mumoles/min/mL with 0-2 forms separated by chromatofocusing. No ChE forms were present within the pH gradient. These results may be significant in contributing to the understanding of the selective toxicity of organophosphorus and carbamate pesticides.
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Volume 61, no. 9, p. 3209, column 2, line 23: "L22165" should read "L22516." [This corrects the article on p. 3208 in vol. 61.].
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The irreversible reaction between liver esterases and the active-site-directed inhibitor bis(4-nitrophenyl)phosphate can be used in vivo both for the estimation of the esterase contents and for the measurement of the esterase degradation rates. A method based on this reaction is described which allows the simultaneous estimation of the rate constants of degradation and synthesis of esterases during a period of change in protein concentration. Rat liver was found to contain about 1 mg of organophosphate-binding esterases per g of fresh tissue while the microsomal fraction contains about 30 mg of esterases per g of microsomal protein. Esterase degradation and de novo synthesis were shown to remain in equilibrium for a period of at least five days following the injection of 10 mg bis(4-nitro-[14C]phenyl)phosphate per kg. The decrease of the relative amount of labeled esterases with time was found to follow first-order kinetics yielding an average esterase degrading constant of 0.0165 h-1 which corresponds to a half-life of 42 h. These data were confirmed by an independent experiment using one of the standard procedures for the estimation of degradation rates: [14C]leucine was incorporated and one of the esterases was subsequently isolated by immuno-precipitation. Using isoelectric focussing and dodecyl sulfate electrophoretic methods, the various esterase isoenzymes appeared to have very similar, if not identical turnover rates. This method for the estimation of the turnover characteristics was applied to evaluate hormone effects on liver esterases. The time course of the contents and the turnover of liver esterases was measured under the influence of glucagon treatment in diabetic rats and under the influence of high doses of insulin. The esterase content decreased faster than the average content of microsomal protein under the influence of glucagon. The reverse effect was observed with insulin-treated rats. Both insulin and glucagon apparently reduced the intracellular esterase turnover in rat liver. Kinetic analysis of the results revealed that insulin mainly lowered the esterase degradation rate, though the rate of esterase synthesis might also have been restricted. In the glucagon-treated rats the de novo synthesis of esterases was strongly reduced.
A full-length cDNA complementary to the rat pancreatic cholesterol esterase mRNA was isolated by screening a rat pancreatic cDNA expression library in lambda gt11 vector with antibodies against the porcine pancreatic cholesterol esterase. The isolated cholesterol esterase cDNA is 2050 bp in length and contains an open reading frame coding for a protein of 612 amino acids. A 20-amino acid hydrophobic leader sequence is predicted, based on the position of the first ATG initiation codon upstream from the sequenced amino terminus of the isolated cholesterol esterase. The cholesterol esterase cDNA was subcloned into a mammalian expression vector, pSVL, for transfection studies. Expression of the cDNA in COS cells resulted in the production of bile salt-stimulated cholesterol esterase. Comparison of the cholesterol esterase cDNA sequence with other proteins revealed that the pancreatic cholesterol esterase is identical to rat pancreatic lysophospholipase. The primary structure of cholesterol esterase displayed no significant homology with other lipases, although the putative lipid interfacial recognition site of G-X-S-X-G is present in the cholesterol esterase sequence. However, the cholesterol esterase sequence revealed a 63-amino-acid domain which is highly homologous to the active site domain of other serine esterases. These data suggest that cholesterol esterase may be a member of the serine esterase supergene family. Analysis of the cholesterol esterase structure also revealed a repetitive sequence enriched with Pro, Asp, Glu, Ser, and Thr residues at the C-terminal end of the protein. This sequence is reminiscent of the PEST-rich sequences in short-lived proteins, suggesting that cholesterol esterase may have a short half-life in vivo. Northern blot hybridization showed that the bile salt-stimulated cholesterol esterase mRNA is present in liver suggesting that this protein may also be synthesized by liver cells.
The presence or absence of the Es-Si esterase (female specific sex-influenced esterase) in rat sera was reexamined by the zymogram technique using agarosegel electrophoresis. It was found that female rat sera of the BN/Kyo strain, which has been typed as the Es-Si esterase negative, display an esterase migrating between the Es-1A esterase and the Es-2C esterase. Using a specific alloantibody to the esterase, it was shown that this esterase is identical to the Es-Si esterase. Thus, BN rats are the first described inbred rats possessing the Es-Si esterase, as well as the Es-1A esterase. Mating experiments between BN rats and SHR rats confirmed a previous demonstration that the presence or absence of the Es-Si esterase is controlled by a single gene locus closely linked to the Es-2 locus where the Es-1 locus also is linked. A further survey with 39 strains by the present methods revealed that besides two sublines of the BN strain, E3/Han, LOU/Max and PVG/Max strains also possess both the ES-1A esterase and the Es-Si esterase. The results indicate that these esterases are controlled by separate gene loci.
The polyester-polyurethane (PUR)-degrading bacterium Comamonas acidovorans TB-35 produces two kinds of esterases, one cell-bound esterase (PUR esterase) and the other secreted in the culture broth (CBS esterase). In this study, the CBS esterase and the two recombinant esterases were purified. Identification of the physical and biochemical properties of the CBS and PUR esterases revealed that they have the same polypeptide from one gene. This finding was supported by the observation that Escherichia coli harboring the PUR esterase gene also produced two kinds of esterases. Though the PUR esterase degraded PUR and poly(diethylene glycol adipate), the soft segment of the PUR, the CBS esterase degraded only poly(diethylene glycol adipate). Furthermore, the hydrophobicity of the CBS esterase was lower than that of the PUR esterase. As the PUR esterase has been previously indicated to possess a PUR-binding domain, it was assumed that structural change around the PUR-binding domain of the CBS esterase was responsible for its inability to degrade PUR.
In Culex pipiens mosquitoes, resistance to organophosphorous insecticides often results from increased detoxification by two types of esterases, A and B, which are closely linked. Overproduction of all esterase B so far investigated (B1, B2, B4, B5 and B6) is from gene amplification. An esterase A gene (esterase A2) has recently been cloned from mosquitoes with the overproduced esterases A2 and B2, and amplification of this gene has also been reported. We describe the cDNA sequences of three additional esterase genes from insecticide-resistant strains of Culex pipiens originating from France and California which show at least 93 per cent homology with the esterase A2 gene sequence. Restriction enzyme mapping shows that the esterase A gene lies within 2.2 kb of the esterase B gene. In mosquitoes with overproduced esterases A2 and B2, the amplification level of esterase A is equal to that of esterase B suggesting that the genes are coamplified. Furthermore, we show that in one strain with an overproduced A esterase (A1), gene amplification cannot account for the increased protein level. This indicates that overproduction of esterases A can be achieved through two different mechanisms: gene amplification and a regulatory mechanism--the nature of which remains to be identified.