Serum paraoxonase is reduced in type 1 diabetic patients compared to non-diabetic, first degree relatives; influence on the ability of HDL to protect LDL from oxidation

Paraoxonase is a serum enzyme with an anti-oxidant function, protecting low density lipoproteins (LDL) from oxidative modifications. Diabetic patients are suggested to be at greater risk of oxidative stress, which may contribute to the significantly higher incidence of vascular disease in this population. Less efficient protection mechanisms may be one feature of the greater susceptibility to oxidation in diabetes. In this context, the present study examined the hypothesis that serum paraoxonase is reduced in type 1 (insulin-dependent) diabetic patients and that the reduction can affect the anti-oxidant capacity of HDL. Serum paraoxonase concentrations and activities were compared in type 1 patients and first degree, non-diabetic relatives with particular attention paid to the confounding effects of paraoxonase gene polymorphisms. In addition, the ability of HDL-paraoxonase to protect low density lipoproteins from oxidation was analysed in an in vitro system. Serum concentrations and enzyme activities of paraoxonase were significantly lower in type 1 patients compared to non-diabetic, first degree relatives. The differences were independent of promoter and coding region polymorphisms, which influence serum concentrations and activities of the enzyme. Overall, paraoxonase concentrations were a mean 13.3+/-4.5% lower (P<0.02) in type 1 patients. Specific activities did not differ between diabetic and non-diabetic groups. The concentration ratios of LDL cholesterol:paraoxonase (1.37+/-0.51 vs. 1.18+/-0.37, P=0.003) and apolipoprotein B:paraoxonase (0.84+/-0.33 vs. 0.71+/-0.40; P=0.012) were significantly higher in diabetic patients, consistent with a reduced capacity to protect LDL from oxidation. In vitro oxidation studies showed that a significantly higher level of lipid hydroperoxides was generated in LDL in the presence of HDL, containing paraoxonase levels equivalent to those of type 1 patients, compared to HDL containing paraoxonase levels equivalent to those of control subjects (mean difference 8.1%, P<0.05). The study demonstrates that serum concentrations of the antioxidant enzyme paraoxonase are significantly lower in type 1 (insulin-dependent) diabetic patients compared to non-diabetic, first-degree relatives, independently of known gene polymorphisms. Concentrations are reduced to an extent that can affect its anti-oxidant capacity. The results are consistent with the contention that modifications to serum paraoxonase in type 1 patients can increase risk of lipoprotein oxidation and, consequently, risk of vascular disease.

AtSPO11-1 is necessary for efficient meiotic recombination in plants

The Saccharomyces cerevisiae Spo11 protein catalyses DNA double-strand breaks (DSBs) that initiate meiotic recombination. The model plant Arabidopsis thaliana possesses at least three SPO11 homologues. T-DNA and ethyl-methane sulfonate mutagenesis allowed us to show that meiotic progression is altered in plants in which the AtSPO11-1 gene is disrupted. Both male and female meiocytes formed very few bivalents. Furthermore, no fully synapsed chromosomes were observed during prophase I. Later, in meiosis I, we observed that chromosomes segregated randomly, leading to the production of a large proportion of non-functional gametes. These meiotic aberrations were associated with a drastic reduction in meiotic recombination. Thus, our data show that initiation of meiotic recombination by SPO11- induced DSBs is a mechanism conserved in plants. Furthermore, unlike Drosophila and Caenorhabditis elegans, but like fungi, SPO11 is necessary for normal synapsis in plants.

Role of esterase gp70 and its influence on growth and development of Dictyostelium discoideum

Gp70 is an esterase originally called crystal protein because of its presence in crystalline structures in aggregation-competent Dictyostelium discoideum cells. Although postulated to break down spore coats, the function of gp70 in vivo was incompletely investigated. Our immunolocalization and biochemical studies of vegetative D. discoideum amoebae show that gp70 was recruited to phagosomes and found in lysosomes. Purified gp70 was effective at hydrolyzing naphthyl substrates with acyl chains typical of lipids and lipopolysaccharides, indicating that the gp70 was involved in digesting endocytosed molecules. The activity of purified gp70 was inhibited by reductants that retarded its electrophoretic mobility and verified the presence of intramolecular disulfide bonds predicted by its amino acid sequence. Compared to wild-type cells, cells overexpressing gp70 were more phagocytically active, had shorter generation times, and produced more fruiting bodies per unit area, while cells lacking gp70 were phagocytically less active with longer doubling times, developed more slowly, and had significantly fewer fruiting bodies per unit area. Consistent with the phenotype of a disrupted metabolism, one-third of the gp70-minus cells were large and multinucleated. Together, these results indicated that despite its crystalline appearance, gp70 was an active esterase involved in both the growth and the development of D. discoideum.

Rabbit serum paraoxonase 3 (PON3) is a high density lipoprotein-associated lactonase and protects low density lipoprotein against oxidation

The paraoxonase gene family contains at least three members: PON1, PON2, and PON3. The physiological roles of the corresponding gene products are still uncertain. Until recently, only the serum paraoxonase/arylesterase (PON1) had been purified and characterized. Here we report the purification, cloning, and characterization of rabbit serum PON3. PON3 is a 40-kDa protein associated with the high density lipoprotein fraction of serum. In contrast to PON1, PON3 has very limited arylesterase and no paraoxonase activities but rapidly hydrolyzes lactones such as statin prodrugs (e.g. lovastatin). These differences facilitated the complete separation of PON3 from PON1 during purification. PON3 hydrolyzes aromatic lactones and 5- or 6-member ring lactones with aliphatic substituents but not simple lactones or those with polar substituents. We cloned PON3 from total rabbit liver RNA and expressed it in mammalian 293T/17 cells. The recombinant PON3 has the same apparent molecular mass and substrate specificity as the enzyme purified from serum. Rabbit serum PON3 is more efficient than rabbit PON1 in protecting low density lipoprotein from copper-induced oxidation. This is the first report that identifies a second PON enzyme in mammalian serum and the first to describe an enzymatic activity for PON3.

Disjunction of homologous chromosomes in meiosis I depends on proteolytic cleavage of the meiotic cohesin Rec8 by separin

It has been proposed but never proven that cohesion between sister chromatids distal to chiasmata is responsible for holding homologous chromosomes together while spindles attempt to pull them toward opposite poles during metaphase of meiosis I. Meanwhile, the mechanism by which disjunction of homologs is triggered at the onset of anaphase I has remained a complete mystery. In yeast, cohesion between sister chromatid arms during meiosis depends on a meiosis-specific cohesin subunit called Rec8, whose mitotic equivalent, Sccl, is cleaved at the metaphase to anaphase transition by an endopeptidase called separin. We show here that cleavage of Rec8 by separin at one of two different sites is necessary for the resolution of chiasmata and the disjunction of homologous chromosomes during meiosis.

Replication-dependent early meiotic requirement for Spo11 and Rad50

Spo11 and the Rad50-Mre11 complex have been indirectly implicated in processes associated with DNA replication. These proteins also have been shown to have early meiotic roles essential for the formation of a programmed DNA double-strand break known in Saccharomyces cerevisiae to initiate meiotic recombination. In both S. cerevisiae and the basidiomycete Coprinus cinereus, spo11 and rad50 mutants are defective in chromosome synapsis during meiosis. Here we demonstrate that a partial restoration of synapsis occurs in C. cinereus spo11 and rad50 mutants if premeiotic DNA replication is prevented. Double mutants were constructed with spo11-1 or rad50-4 and another mutant, spo22-1, which does not undergo premeiotic DNA replication. In both cases, we observed an increase in the percentage of nuclei containing synaptonemal complex (SC) structures, with concomitant decreases in the percentage of nuclei containing axial elements (AE) only or no structures. Both types of double mutants demonstrated significant increases in the average numbers of AE and SC, although SC-containing nuclei did not on average contain more AE than did nuclei showing no synapsis. Our results show that Spo11-induced recombination is not absolutely required for synapsis in C. cinereus, and that the early meiotic role of both Spo11 and Rad50 in SC formation partially depends on premeiotic S phase. This dependency likely reflects either a requirement for these proteins imposed by the premeiotic replication process itself or a requirement for these proteins in synapsis when a sister chromatid (the outcome of DNA replication) is present.

Viability of cryopreserved semilunar valves: an evaluation of cytosolic and mitochondrial activities

BACKGROUND

Despite long-standing, widespread use of cryopreserved allografts, the basic cellular biology of these tissues is still yet unknown. The present investigation was undertaken to study cryopreserved heart valves from the standpoint of cytosolic esterase and mitochondrial dehydrogenase activities.

METHODS

Cryopreserved porcine aortic cusps were observed in an unfixed fresh condition with a confocal laser scanning microscope using fluorescent dye. Porcine cusps and cultured human umbilical vein endothelial cells were divided into three groups, including fresh, cold-preserved, and cryopreserved specimens, and cytosolic esterase activity and mitochondrial dehydrogenase activity were analyzed in each.

RESULTS

Confocal laser scanning microscope findings disclosed a widely distributed fluorescence in the cusp. Cytosolic esterase activity within human umbilical vein endothelial cells (28%+/-9.0%) after cryopreservation was significantly less than that it was in the cusps (72%+/-21%). Mitochondrial dehydrogenase activity of cryopreserved human umbilical vein endothelial cells and that of cusps fell to 44%+/-6.1% and 64%+/-17% respectively; the difference between the two values was not significant.

CONCLUSIONS

Cryopreservation appeared to produce serious damage to cytosolic and mitochondrial functions of endothelial cells. The cytosolic function of cusps, mainly consisting of fibroblasts, was comparatively preserved after cryopreservation, but mitochondrial function of the cusps was more diminished.

Esterases in marine dinoflagellates and resistance to the organophosphate insecticide parathion

Esterases are involved in the susceptibility or resistance of organisms to organophosphate pesticides. We have examined the action of parathion on the marine dinoflagellates Crypthecodinium cohnii and Prorocentrum micans by looking at their esterases. One-dimensional gel electrophoresis, immunoblotting and cytochemistry plus image analysis were used to characterize the nature and distribution of the enzymes. Esterases were found in both species, but there appeared to be no particular intracellular localization. The esterase activity of the heterotrophic species Crypthecodinium cohnii was 30-fold greater than that of the autotrophic Prorocentrum micans and had an antigenic site in common with mosquito esterase. The resistance of Crypthecodinium cohnii to parathion was specific and reversible. Less parathion entered the parathion-resistant Crypthecodinium cohnii cells than the untreated control cells. Parathion-resistant cell extracts of Crypthecodinium cohnii analyzed after immunoblotting also contained an additional band of esterase activity. These results confirm the importance of esterases in toxicological studies of organophosphate insecticides, especially those of marine dinoflagellates.

Multiple roles of Spo11 in meiotic chromosome behavior

Spo11, a type II topoisomerase, is likely to be required universally for initiation of meiotic recombination. However, a dichotomy exists between budding yeast and the animals Caenorhabditis elegans and Drosophila melanogaster with respect to additional roles of Spo11 in meiosis. In Saccharomyces cerevisiae, Spo11 is required for homolog pairing, as well as axial element (AE) and synaptonemal complex (SC) formation. All of these functions are Spo11 independent in C.elegans and D.melanogaster. We examined Spo11 function in a multicellular fungus, Coprinus cinereus. The C.cinereus spo11-1 mutant shows high levels of homolog pairing and occasionally forms full-length AEs, but no SC. In C.cinereus, Spo11 is also required for maintenance of meiotic chromosome condensation and proper spindle formation. Meiotic progression in spo11-1 is aberrant; late in meiosis basidia undergo programmed cell death (PCD). To our knowledge, this is the first example of meiotic PCD outside the animal kingdom. Ionizing radiation can partially rescue spo11-1 for both AE and SC formation and viable spore production, suggesting that the double-strand break function of Spo11 is conserved and is required for these functions.

Human serum paraoxonases (PON1) Q and R selectively decrease lipid peroxides in human coronary and carotid atherosclerotic lesions: PON1 esterase and peroxidase-like activities

BACKGROUND

Human serum paraoxonase (PON1) exists in two polymorphic forms: one that differs in the amino acid at position 192 (glutamine and arginine, Q and R, respectively) and the second one that differs in the amino acid at position 55 (methionine and leucine, M and L, respectively). PON1 protects LDL from oxidation, and during LDL oxidation, PON1 is inactivated.

METHODS AND RESULTS

The present study compared PON1 isoforms Q and R for their effect on lipid peroxide content in human coronary and carotid lesions. After 24 hours of incubation with PON1Q or PON1R (10 arylesterase units/mL), lipid peroxides content in both coronary and carotid lesion homogenates (0.1 g/mL) was reduced up to 27% and 16%, respectively. The above incubation was associated with inactivation of PON1Q and PON1R by 15% and 45%, respectively. Lesion cholesteryl linoleate hydroperoxides and cholesteryl linoleate hydroxides were hydrolyzed by PON1 to yield linoleic acid hydroperoxides and linoleic acid hydroxides. Furthermore, lesion and pure linoleic acid hydroperoxides were reduced to yield linoleic acid hydroxides. These results thus indicate that PON1 demonstrates esterase-like and peroxidase-like activities. Recombinant PON1 mutants in which the PON1-free sulfhydryl group at cysteine-284 was replaced with either alanine or serine were no longer able to reduce lipid peroxide content in carotid lesions.

CONCLUSIONS

We conclude that PON1 may be antiatherogenic because it hydrolyzes lipid peroxides in human atherosclerotic lesions.

Progression of meiotic DNA replication is modulated by interchromosomal interaction proteins, negatively by Spo11p and positively by Rec8p

Spo11p is a key mediator of interhomolog interactions during meiosis. Deletion of the SPO11 gene decreases the length of S phase by approximately 25%. Rec8p is a key coordinator of meiotic interhomolog and intersister interactions. Deletion of the REC8 gene increases S-phase length, by approximately 10% in wild-type and approximately 30% in a spo11Delta background. Thus, the progression of DNA replication is modulated by interchromosomal interaction proteins. The spo11-Y135F DSB (double strand break) catalysis-defective mutant is normal for S-phase modulation and DSB-independent homolog pairing but is defective for later events, formation of DSBs, and synaptonemal complexes. Thus, earlier and later functions of Spo11 are defined. We propose that meiotic S-phase progression is linked directly to development of specific chromosomal features required for meiotic interhomolog interactions and that this feedback process is built upon a more fundamental mechanism, common to all cell types, by which S-phase progression is coupled to development of nascent intersister connections and/or related aspects of chromosome morphogenesis. Roles for Rec8 and/or Spo11 in progression through other stages of meiosis are also revealed.

Comparison of the role of esterases in the differential age-related sensitivity to chlorpyrifos and methamidophos

More than 30 years ago, scientists recognized that, at a given dosage, the young rat was more sensitive than the adult to the toxicity of many organophosphorus, anticholinesterase pesticides. This observation went basically unexamined until recently. Renewed interest has emerged in scrutinizing this age-related sensitivity to pesticides, especially in light of the many new pesticides which are currently marketed. Our laboratory has been involved in comparing the age-related sensitivity of young and adult rats to chlorpyrifos [Dursban, Lorsban; O,O-diethyl O-(3,5,6-trichloro-2-pyridyl) phosphorothioate] and methamidophos (Monitor; O,S-dimethyl phosphoamidothioate). Using chlorpyrifos, there is marked age-related sensitivity: direct oral dosing of the preweanling rat (postnatal day 17; PND17) with chlorpyrifos causes a toxic response (defined either behaviorally or biochemically) at a approximately 5-fold lower dosage than in adults (oral, maximum tolerated dose for the PND17 is 20 mg/kg versus 100 mg/kg for the adult). Other studies have indicated that the rat detoxifies chlorpyrifos and its oxon by binding to carboxylesterases and hydrolysis by A-esterases. The young rat is deficient in both these detoxification enzymes, which may explain the increased sensitivity of the young to chlorpyrifos toxicity. The age-related pattern for methamidophos is distinctly different: the oral, maximum tolerated dose is the same (8 mg/kg) whether the animal is 17 days old or an adult. We present data which indicate that methamidophos is not detoxified appreciably either in vivo or in vitro by A-esterases or carboxylesterases. Therefore, we submit the following hypothesis: organophosphorus pesticides, like chlorpyrifos, which are detoxified via A-esterases or carboxylesterases are more likely to exhibit age-related differences in sensitivity than pesticides which are not detoxified via these routes.

Rapid esterase-sensitive breakdown of polysorbate 80 and its impact on the plasma pharmacokinetics of docetaxel and metabolites in mice

We have developed and validated an analytical methodology for the quantification of docetaxel and its four major human oxidation metabolites in mouse plasma. We have used this procedure to study the pharmacokinetics and metabolism of docetaxel in female FVB mice, receiving 2.5, 10, or 33 mg/kg of docetaxel by i.v. injection. We have also studied the pharmacokinetics of polysorbate 80, because it was shown previously that the vehicle substance Cremophor EL, which is used in the formulation of paclitaxel, exerts a profound effect on the pharmacokinetics of this compound. Linear pharmacokinetics of docetaxel was observed at dose levels between 2.5 and 10 mg/kg, where plasma levels corresponded to those in patients receiving the maximum tolerated dose. At the highest dose level of 33 mg/kg, a deviation from the linear kinetics was observed. Compared with humans, mice could tolerate much higher plasma levels, suggesting that the toxic side effects are related to a certain plasma threshold concentration instead of area under the curve or Cmax. At the highest dose level, three docetaxel metabolites could be detected in the plasma samples of mice for up to 4 h after drug administration. The hydroxy metabolite of the tert-butoxy group (metabolite II) was the major metabolite, followed by the two epimeric hydroxyoxazolone-type compounds (metabolites I and III). A fourth putative metabolite (e.g., the cyclic oxazolidinedione derivative) was not detected. Because of rapid degradation of polysorbate 80 by esterases in plasma, the concentration of this vehicle substance declined very rapidly. Consequently, this substance was not able to interfere in the disposition of docetaxel.

Does paraoxonase play a role in susceptibility to cardiovascular disease?

Human serum paraoxonase (PON1) is an esterase that is bound to high-density lipoproteins (HDLs). It can hydrolyze organophosphates and its activity is inversely related to atherosclerosis. Some studies also suggest that a relationship exists between polymorphisms of the gene that encodes paraoxonase and coronary heart disease (CHD), whereas other studies, in different populations, have not found such an association. One mechanism by which certain PON1 allozymes might protect against atherosclerosis is by inhibition of the oxidation of HDL and low-density lipoprotein (LDL). Experimental studies suggest that this protection is associated with the ability of PON1 to hydrolyze specific lipid peroxides in oxidized lipoproteins. Interventions that preserve or enhance PON1 activity, as well as manipulations of PON1 polymorphisms, might help delay the onset of CHD.

Human serum Paraoxonase/Arylesterase's retained hydrophobic N-terminal leader sequence associates with HDLs by binding phospholipids : apolipoprotein A-I stabilizes activity

In serum, human paraoxonase/arylesterase (PON1) is found exclusively associated with high density lipoprotein (HDL) and contributes to its antiatherogenic properties by inhibiting low density lipoprotein (LDL) oxidation. Difficulties in purifying PON1 from apolipoprotein A-I (apoA-I) suggested that PON1's association with HDL may occur through a direct binding between these 2 proteins. An unusual property of PON1 is that the mature protein retains its hydrophobic N-terminal signal sequence. By expressing in vitro a mutant PON1 with a cleavable N-terminus, we demonstrate that PON1 associates with lipoproteins through its N-terminus by binding phospholipids directly rather than binding apoA-I. Nonetheless, apoA-I stabilized arylesterase activity more than did phospholipid alone, apoA-II, or apoE. Consequently, we studied the role of apoA-I in PON1 expression and HDL association in mice genetically deficient in apoA-I. Though present in HDL fractions at decreased levels, PON1 arylesterase activity was less stable than in control mice. Furthermore, PON1 could be competitively removed from HDL by phospholipids, suggesting that PON1's retained N-terminal peptide allows transfer of the enzyme between phospholipid surfaces. Thus, our data suggest that PON1 is stabilized by apoA-I, and its binding to HDL and physiological distribution are dependent on the direct binding of the retained hydrophobic N-terminus to phospholipids optimally presented in association with apoA-I.

On the physiological role(s) of the paraoxonases

In recent years several lines of evidence have indicated that serum paraoxonase (PON1), and perhaps other mammalian paraoxonases, act as important guardians against cellular damage from toxic agents, such as organophosphates, oxidized lipids in the plasma low density lipoproteins (LDL), and against bacterial endotoxins. For some of these protective activities but not all, PON1 requires calcium ion. The catalyzed chemical reactions generally seem to be hydrolytic, but for some types of protection this may not be so. Several other metals have very high affinity for PON1 and may displace calcium. Replacement or substitution of calcium by other metals could extend the range of catalytic properties and the substrate specificity of the paraoxonases, as it does for the mammalian DFPases. Although this Third International Meeting on Esterases Reacting with Organophosphorus Compounds focuses on the organophosphatase activities of paraoxonase and related enzymes, it is important to also briefly review some of the current directions in several laboratories searching for additional functions of the paraoxonases to extend our understanding of the properties of this family of enzymes which now seem to have both physiological and toxicological importance.

Isoesterases related to cell differentiation in plant tissue culture

Normal, habituated and transformed in vitro tissue lines of sugar beet (Beta vulgaris L.), horseradish (Armoracia lapathifolia Gilib.) and potato (Solanum tuberosum L.) were studied with regard to isoesterase patterns. Isoenzymes were separated in gradient gels (5-12%) of polyacrylamide and by isoelectric focussing in pH range 4-9. 1- and 2-naphtylacetate were used as substrates of broad spectrum which cover also esterases (arylesterases and carboxylesterases) reacting with organophosphorous compounds. Distinct isoesterase patterns were noticed in sugar beet normal, habituated and crown gall tumour tissues. Horseradish tumour and teratoma, on the contrary, differed only in one anodic isoenzyme. Even the malformed shoots and unorganised tissue of teratoma had the same patterns. In potato tuber tissue, change in isoesterase pattern, characterised by disappearance of a dominant dark area, was observed during tumour development. The gradient gels gave more stable and reproducible isoenzyme patterns than isoelectric focussing.

The role of paraoxonase (PON1) in the detoxication of organophosphates and its human polymorphism

In human populations, serum paraoxonase (PON1) exhibits a substrate dependent polymorphism. The Arg192 isoform hydrolyzes paraoxon rapidly but diazoxon, soman and especially sarin slowly. On the other hand, the Gln192 isoform hydrolyzes paraoxon slowly, but diazoxon, soman and sarin more rapidly than the Arg192 isoform. Our experiments with a mouse model system have convincingly shown that PON1 plays a major role in the detoxication of organophosphate (OP) compounds processed through the P450/PON1 pathway. Recent studies have also shown that PON1 plays an important role in the metabolism of oxidized lipid compounds. Currently, there is an effort underway to identify genes and polymorphisms that play an important role in 'environmental susceptibility'. The PON1 polymorphism has been cited as a prime example of such a genetic polymorphism. The advent of the polymerase chain reaction (PCR) for DNA amplification with improvements, modifications and automation has provided a very convenient way to do individual genotyping. It is tempting to set up large scale PCR analyses of populations to determine individuals at risk for environmental exposures affected by the PON1 polymorphism. In fact, a number of such studies have already been carried out in examining the relationship of the PON1 polymorphism to vascular disease. We advocate the use of a high throughput two-dimensional enzyme assay that provides both PON1 genotype and phenotype (PON1 status). The high level of variation of gene expression within each genetic class in humans, together with our animal model studies indicate that it is very important to determine PON status as opposed to PON1 genotype alone. Experiments in rats and mice have shown that injection of PON1 purified from rabbit serum by the i.v., i.p. or i.m. route, significantly increases PON1 activities in rodents' plasma. Under these conditions, the acute toxicity (assessed by the degree of acetylcholinesterase inhibition) of paraoxon and chlorpyrifos oxon is significantly decreased, compared to control animals. Protection is maximal when PON1 is administered before the OPs, but still occurs when PON1 is utilized as a post-exposure treatment. Furthermore, protection by PON1 is also provided toward the parent compound chlorpyrifos. Pon1-knockout mice display a much greater sensitivity to chlorpyrifos oxon toxicity than wild mice. However, the acute toxicity of guthion, which is not a substrate for PON1, does not differ between knockout and wild mice. These observations underline the importance of considering both genetic variability of enzyme isoform as well as enzyme level (PON1 status) and the developmental time course of appearance of PON1 in developing risk assessment models.

Organophosphorus acid anhydrolase in slime mold, duckweed and mung bean: a continuing search for a physiological role and a natural substrate

Recently, and for the first time, a diisopropylphosphorofluoridate (DFP)-hydrolyzing enzyme, i.e. an organophosphorus acid anhydrolase (OPAA), has been reported in a plant-source. Based on this and other suggestive evidence, the ability of three plant sources and a protist to hydrolyze DFP and 1,2,2-trimethylpropyl methylphosphonofluoridate (Soman) were tested, and the effects of Mn2+ and ethylenediamine tetraacetate (EDTA) on this activity. The plants are duckweed (Lemna minor), giant duckweed (Spirodela oligorhiza), and germinated mung bean (Vigna radiata); the protist is a slime mold (Dictyostelium discoidium). The tests are based on a crude classification of OPAAs as 'squid type' (DFP hydrolyzed more rapidly than Soman) and all of the others termed by us, with questionable justification, as 'Mazur type' (Soman hydrolyzed more rapidly than DFP). Of the two duckweeds, Spirodela oligorhiza hydrolyzes Soman but not DFP, and Lemna minor does not hydrolyze either substrate. In contrast to the report of Yu and Sakurai, mung bean does not hydrolyze DFP and hydrolyzes Soman with a 5-fold stimulation by Mn2+ and a marked inhibition by EDTA. The slime mold hydrolyzes Soman more rapidly than DFP (but does hydrolyze DFP) and the hydrolysis is Mn2+ stimulated. The failure of these plant sources to hydrolyze DFP is similar to the behavior of OPAA from Bacillus stearothermophilus.

Pathogen-induced elicitin production in transgenic tobacco generates a hypersensitive response and nonspecific disease resistance

The rapid and effective activation of disease resistance responses is essential for plant defense against pathogen attack. These responses are initiated when pathogen-derived molecules (elicitors) are recognized by the host. We have developed a strategy for creating novel disease resistance traits whereby transgenic plants respond to infection by a virulent pathogen with the production of an elicitor. To this end, we generated transgenic tobacco plants harboring a fusion between the pathogen-inducible tobacco hsr 203J gene promoter and a Phytophthora cryptogea gene encoding the highly active elicitor cryptogein. Under noninduced conditions, the transgene was silent, and no cryptogein could be detected in the transgenic plants. In contrast, infection by the virulent fungus P. parasitica var nicotianae stimulated cryptogein production that coincided with the fast induction of several defense genes at and around the infection sites. Induced elicitor production resulted in a localized necrosis that resembled a P. cryptogea-induced hypersensitive response and that restricted further growth of the pathogen. The transgenic plants displayed enhanced resistance to fungal pathogens that were unrelated to Phytophthora species, such as Thielaviopsis basicola, Erysiphe cichoracearum, and Botrytis cinerea. Thus, broad-spectrum disease resistance of a plant can be generated without the constitutive synthesis of a transgene product.

The role of phosphotriesterases in the detoxication of organophosphorus compounds

The enzymes that hydrolyze organophosphorus compounds are called phosphotriesterases. The presence of phosphotriesterases has been described in a variety of tissues. The physiological role of these enzymes is not known, although a clear correlation exists between the levels of phosphotriesterases and susceptibility of the species to the toxic effects of organophosphorus compounds. Thus, mammals that possess high levels of phosphotriesterases in serum and liver are more tolerant to the toxic effects of these compounds than birds and insects - these being species considered lacking of phosphotriesterases. Because most of these enzymes are not well characterized, they are usually differentiated according to their different patterns of response to activators and/ or inhibitors. Phosphotriesterases usually depend of divalent cations and therefore EDTA usually inhibits them. A peculiar EDTA-resistant phosphotriesterase has been described in serum albumin. The biotechnological and therapeutical applications of phosphotriesterases are currently subject to study.

Schizosaccharomyces pombe rad32 protein: a phosphoprotein with an essential phosphoesterase motif required for repair of DNA double strand breaks

The Schizosaccharomyces pombe Rad32 protein is required for repair of DNA double strand breaks, minichromosome stability and meiotic recombination. We show here that the Rad32 protein is phosphorylated in a cell cycle-dependent manner and during meiosis. The phosphorylation is not dependent on the checkpoint protein Rad3. Analysis of a partially purified protein preparation indicates that Rad32 is likely to act in a complex. Characterisation of the rad32-1 mutation and site-directed mutagenesis indicate that three aspartate residues in the conserved phosphoesterase motifs are important for both mitotic and meiotic functions, namely response to UV and ionising radiation and spore viability.

Human serum paraoxonase

1. Human serum paraoxonase (PON1) is a Ca2+-dependent 45-kDa glycoprotein that is associated with high density lipoprotein (HDL). 2. PON1 hydrolyzes organophosphate (OP) insecticides and nerve gases and is responsible for determining the selective toxicity of these compounds in mammals. 3. PON1 has two genetic polymorphisms giving rise to amino acid substitutions at positions 55 and 192. The position-192 polymorphism is the major determinant of the PON1 activity polymorphism. However, the position-55 polymorphism also modulates activity. 4. Genotyping individuals for both PON1 polymorphisms may provide a method for identifying those most at risk of OP poisoning. The effect of the PON1 polymorphisms on activity may explain why some Gulf War veterans have developed Gulf War syndrome and some have not, despite similar OP exposure. 5. PON1 may also be a determinant of resistance to the development of atherosclerosis by protecting lipoproteins against oxidative modification, perhaps by hydrolyzing phospholipid hydroperoxides. 6. The PON 1 polymorphisms are important in determining the capacity of HDL to protect low density lipoprotein against oxidative modification in vitro, which may explain the relation between the PON1 alleles and coronary heart disease in case-control studies.

Mice lacking serum paraoxonase are susceptible to organophosphate toxicity and atherosclerosis

Serum paraoxonase (PON1) is an esterase that is associated with high-density lipoproteins (HDLs) in the plasma; it is involved in the detoxification of organophosphate insecticides such as parathion and chlorpyrifos. PON1 may also confer protection against coronary artery disease by destroying pro-inflammatory oxidized lipids present in oxidized low-density lipoproteins (LDLs). To study the role of PON1 in vivo, we created PON1-knockout mice by gene targeting. Compared with their wild-type littermates, PON1-deficient mice were extremely sensitive to the toxic effects of chlorpyrifos oxon, the activated form of chlorpyrifos, and were more sensitive to chlorpyrifos itself. HDLs isolated from PON1-deficient mice were unable to prevent LDL oxidation in a co-cultured cell model of the artery wall, and both HDLs and LDLs isolated from PON1-knockout mice were more susceptible to oxidation by co-cultured cells than the lipoproteins from wild-type littermates. When fed on a high-fat, high-cholesterol diet, PON1-null mice were more susceptible to atherosclerosis than their wild-type littermates.

The apeE gene of Salmonella typhimurium encodes an outer membrane esterase not present in Escherichia coli

Salmonella typhimurium apeR mutations lead to overproduction of an outer membrane-associated N-acetyl phenylalanine beta-naphthyl ester-cleaving esterase that is encoded by the apeE gene (P. Collin-Osdoby and C. G. Miller, Mol. Gen. Genet. 243:674-680, 1994). This paper reports the cloning and nucleotide sequencing of the S. typhimurium apeE gene as well as some properties of the esterase that it encodes. The predicted product of apeE is a 69.9-kDa protein which is processed to a 67-kDa species by removal of a signal peptide. The predicted amino acid sequence of ApeE indicates that it is a member of the GDSL family of serine esterases/lipases. It is most similar to a lipase excreted by the entomopathogenic bacterium Photorhabdus luminescens. The Salmonella esterase catalyzes the hydrolysis of a variety of fatty acid naphthyl esters and of C6 to C16 fatty acid p-nitrophenyl esters but will not hydrolyze peptide bonds. A rapid diagnostic test reported to be useful in distinguishing Salmonella spp. from related organisms makes use of the ability of Salmonella to hydrolyze the chromogenic ester substrate methyl umbelliferyl caprylate. We report that the apeE gene product is the enzyme in Salmonella uniquely responsible for the hydrolysis of this substrate. Southern blot analysis indicates that Escherichia coli K-12 does not contain a close analog of apeE, and it appears that the apeE gene is contained in a region of DNA present in Salmonella but not in E. coli.

Evidence for a paraoxonase-independent inhibition of low-density lipoprotein oxidation by high-density lipoprotein

One mechanism by which plasma high-density lipoprotein (HDL) may protect against atherogenesis is by inhibiting the oxidation of low-density lipoprotein (LDL). Recent evidence suggests that paraoxonase, an HDL-associated, calcium-dependent enzyme, may be responsible for the antioxidant action of HDL (Mackness et al., Atherosclerosis 1993;104:129; Mackness et al., FEBS Lett 1991;286:152; Watson et al., J Clin Invest 1995;96:2882; Navab et al., Arterio Thromb Vasc Biol 1996;16:831); in particular, paraoxonase activity inhibits the formation of 'minimally oxidized' LDL by hydrolyzing biologically active oxidized phospholipids (Watson et al., J Clin Invest 1995;96:2882; Navab et al., Arterio Thromb Vasc Biol 1996;16:831). However, antioxidant effects of HDL have also been demonstrated under calcium-free conditions, arguing that this enzyme may not be the only mechanism by which HDL inhibits LDL oxidation (Tribble et al., J Lipid Res 1995;36:2580). Here we have evaluated the role of paraoxonase in prevention of LDL oxidation by using HDL subfractions, isolated from human serum or EDTA-plasma, which display markedly different levels of paraoxonase activity; the abilities of modified forms of HDL to prevent LDL oxidation by cultured human (THP-1) macrophages were also assessed. Paraoxonase activity was substantially lower in HDL prepared from plasma compared to serum HDL; moreover, virtually all of the lipoprotein-associated paraoxonase activity was located in the HDL3 fraction, with HDL2 retaining only 1-5% of the total activity. Despite possessing 5-fold differences in paraoxonase activity, HDL3 isolated from plasma or serum was equally effective in inhibiting LDL oxidation by THP-1 macrophages; furthermore, although plasma HDL3 was more protective than plasma HDL2, the latter did significantly inhibit LDL oxidation. Non-paraoxonase antioxidant constituents of plasma HDL3 were investigated further. ApoHDL3, the totally delipidated form of HDL3, was much less effective than native HDL3; when examined individually, purified apolipoprotein A-II gave greater protection than apo A-I, although this effect was not evident in apo A-II-enriched HDL3. Partial delipidation of HDL3, which removes both neutral lipids and alpha-tocopherol, did not significantly diminish its ability to inhibit LDL oxidation by THP-1 macrophages; phospholipid vesicles prepared from partially delipidated HDL3 also inhibited LDL oxidation effectively. We conclude that, in this model of cellular LDL oxidation, the phospholipid fraction of HDL exerts inhibitory effects which are independent of HDL paraoxonase activity.

Biochemistry of esterases associated with organophosphate resistance in Lucilia cuprina with comparisons to putative orthologues in other Diptera

Esterase activities associated with organophosphate insecticide resistance in the Australian sheep blowfly, Lucilia cuprina, are compared with similar activities in other Diptera. The enzymes making the major contribution to methyl butyrate hydrolysis ("ali-esterase") in L. cuprina, M. domestica, and D. melanogaster comigrate during electrophoresis. The enzymes in L. cuprina and D. melanogaster correspond to the naphthyl acetate hydrolyzing E3 and EST23 isozymes of those species. These and previously published data suggest that the ali-esterases of all three species are orthologous. Strains of L. cuprina fall into four groups on the basis of quantitative determinations of their ali-estesterase, OP hydrolase, and malathion carboxylesterase activities and these groups correspond to their status with respect to two types of OP resistance. Strains susceptible to OP's have high ali-esterase, low OP hydrolase, and intermediate MCE activities; those resistant to malathion but not diazinon have low ali-esterase, intermediate OP hydrolase, and high MCE activities; those resistant to diazinon but not malathion have low ali-esterase, high OP hydrolase, and low MCE activities; those resistant to both OPs have low ali-esterase, high OP hydrolase, and high MCE activities. The correlated changes among the three biochemical and two resistance phenotypes suggest that they are all properties of one gene/enzyme system; three major allelic variants of that system explain OP susceptibility and the two types of OP resistance. Models are proposed to explain the joint contribution of OP hydrolase and MCE activities to malathion resistance and the invariant association of low ali-esterase and elevated OP hydrolase activities in either type of resistance.

Gliotactin, a novel transmembrane protein on peripheral glia, is required to form the blood-nerve barrier in Drosophila

Peripheral glia help ensure that motor and sensory axons are bathed in the appropriate ionic and biochemical environment. In Drosophila, peripheral glia help shield these axons against the high K+ concentration of the hemolymph, which would largely abolish their excitability. Here, we describe the molecular genetic analysis of gliotactin, a novel transmembrane protein that is transiently expressed on peripheral glia and that is required for the formation of the peripheral blood-nerve barrier. In gliotactin mutant embryos, the peripheral glia develop normally in many respects, except that ultrastructurally and physiologically they do not form a complete blood-nerve barrier. As a result, peripheral motor axons are exposed to the high K+ hemolymph, action potentials fail to propagate, and the embryos are nearly paralyzed.

Esterase activity in the olfactory sensilla of the silkmoth Antheraea polyphemus

We studied in individual males of Antheraea polyphemus the activity of the sensillar esterase, a pheromone-degrading enzyme present in the sensillum lymph surrounding the olfactory receptor cells. In parallel, receptor potentials from single pheromone-sensitive sensilla trichodea were recorded. Our screening revealed a large variability of the enzyme activity in individuals with similar electrophysiological responses. In some moths the sensillar esterase was not detectable, i.e. present with 100-fold less activity. However, such variable esterase activity showed no correlation to the time course of the receptor potential. Thus, enzymatic pheromone degradation does not seem to be involved in the rapid pheromone inactivation at the end of the stimulus, but rather serves as the final pheromone sequestration step.

Dominant chymotrypsin-like esterase activity in human lymphocyte granules is mediated by the serine carboxypeptidase called cathepsin A-like protective protein

We identified a chymotrypsin-like activity in the granules of IL-2 lymphokine-activated killer (LAK) cells and a NK cell line (YT) that reacted preferentially with the oligopeptide substrate succinyl-Phe-Leu-Phe-thiobenzyl ester (Suc-Phe-Leu-Phe-SBzl). The enzyme was isolated by detergent extraction of sedimented cytotoxic granules and then by a sequence of sieve, hydrophobic, and anion exchange chromatography. On SDS-PAGE, the protein migrated at 42 kDa in nonreduced form and became two bands (31 and 19 kDa, respectively) after reduction. Amino-terminal sequencing of the reduced protein bands revealed 100% homology with cathepsin A-like protective protein (CAPP), a lysosomal enzyme that expresses serine carboxypeptidase and deamidase activities. The carboxypeptidase activity of lymphocyte CAPP was verified by showing that the protease preferred hydrophobic amino acids in the penultimate position of the C terminus (i.e., cleaved arginine from dansyl-Phe-Leu-Arg). The presence of lymphocyte CAPP in secretory lysosomes was demonstrated by showing that Suc-Phe-Leu-Phe-SBzl activity co-migrated with tryptase and Asp-ase activities on Percoll density gradients and that 95% of the Suc-Phe-Leu-Phe-SBzl activity in granule fractions of cavitated YT cells could be immunoprecipitated with an anti-CAPP antiserum. In addition, calcium ionophore-stimulated YT cells were shown to secrete immunoprecipitable CAPP. As proposed for platelets, lymphocyte CAPP may be secreted to function extracellularly by inactivating bioactive peptides.

Role of membrane associated serine esterase in the activation of phospholipase A2 by calcium ionophore (A23187) in pulmonary arterial smooth muscle cells

Exposure of rabbit pulmonary arterial smooth muscle cells to 10 microM of the calcium ionophore A23187 dramatically stimulates cell membrane-associated phospholipase A2 activity and arachidonic acid release. In addition, A23187 also enhances cell membrane-associated serine esterase activity. Serine esterase inhibitors phenylmethylsulfonylfluoride and diisopropyl fluorophosphate prevent the increase in serine esterase and phospholipase A2 activities and arachidonic acid release caused by A23187. A23187 still stimulated serine esterase and phospholipase A2 activities and arachidonic acid release in cells pretreated with nominal Ca2+ free buffer. Treatment of the cell membrane with A23187 does not cause any appreciable change in serine esterase and phospholipase A2 activities. Pretreatment of the cells with actinomycin D or cycloheximide did not prevent the increase in the cell membrane associated serine esterase and phospholipase A2 activities, and arachidonic acid release caused by A23187. These results suggest that (i) a membrane-associated A2 activity (ii) in addition to the presence of extracellular Ca2+, release of Ca2+ from intracellular storage site(s) by A23187 also appears to play a role in stimulating the cell membrane-associated serine esterase and phospholipase A2 activities does not appear to require new RNA or protein synthesis.

The selection and genetic analysis of esterase electromorphs in an organophosphate-resistant strain of Culex pipiens from Italy

An Italian organophosphate-resistant strain of Culex pipiens (Lucca) was found to be polymorphic for elevated and nonelevated esterases. Selection for high esterase activity produced a strain homozygous for elevated esterases A2 and B2. Selection for low activity produced a strain homozygous for nonelevated esterases, A4i and B1i. Crossing experiments showed that A2 and B2 are coded by separate but closely linked genes, as are A4i and B1i. Results indicate that elevated A2 and nonelevated A4i are alleles of a single gene (Est-3 locus), as are elevated B2 and nonelevated B1i (Est-2 locus). Selection for electromorph variants gave four elevated A variants and three elevated B variants. These esterases were not selected in the field. In Lucca, A2 and B2 replaced A1, suggesting a selective advantage to the former over the latter in the presence of chlorpyrifos. It is hypothesized that the degree of amplification is an important factor in the selection of a particular esterase electromorph as a resistance mechanism and that migrating individuals with amplified genes could have an advantage when invading a population under selection.

The esterases: perspectives and problems

Many proteins capable of hydrolysing esters are present in biological material of all kinds (microorganisms, plants, invertebrates and vertebrates). Some serve, as indicated by their substrate specificity and distribution within organisms, a defined biological function. However for most esterases a rather general substrate specificity is found indicating that they may have a broad biological function. Their properties will be briefly reviewed with particular emphasis on inhibitors. The mechanism of hydrolysis of esters by many carboxylesterases (B-esterases) is well established largely due to the reaction of OP compounds with their catalytic centre. For others, such as enzymes hydrolysing (i) OP compounds and/or (ii) carboxyl esters which are not inhibited by a time and temperature dependent reaction by OP compounds, reaction mechanisms are still conjecture. The purpose of this presentation is to explore similarities and differences between the esterases and to discuss possible routes for progress in the A-esterase group.

Role of serine esterase in A23187-mediated activation of phospholipase A2 in pulmonary endothelium

To test the hypothesis that an endothelial cell membrane-associated serine esterase is involved in regulating phospholipase A2 (PLA2), we studied the effect of the calcium ionophore A23187 on intracellular PLA2 activity and arachidonic acid (AA) release in bovine pulmonary arterial endothelial cells. Exposure of these cells to A23187 causes a concentration-dependent increase in PLA2 activity and [14C]AA release. In addition to increasing PLA2 activity and AA release, A23187 enhances the activity of endothelial cell membrane-associated serine esterase that acts on the synthetic substrate N alpha-p-tosyl-L-arginine methyl ester. Serine esterase inhibitors, such as phenylmethylsulfonyl fluoride and diisopropyl fluorophosphate, prevent the A23187-mediated increase in serine esterase activity, PLA2 activity, and AA release. Pretreatment of the cells with actinomycin D or cycloheximide does not prevent the A23187-mediated increase in AA release, serine esterase activity, or PLA2 activity. The membrane-associated serine esterase activity directly correlates with membrane PLA2 activity. These results suggest that a membrane-associated serine esterase plays a pivotal role in regulating PLA2 activity after exposure to A23187.

Cytotoxicity of activated platelets to autologous red blood cells

Gel-filtered human platelets exerted lytic activity on autologous red blood cells (RBC) when they were coincubated at 37 degrees C with platelet-activating agents, such as thrombin, collagen, ADP, LPS or PMA in the absence of plasma. Lysis of activated platelets themselves did not occur during the incubation period examined. Morphological observations showed that RBC exposed to thrombin-activated platelets were fragmented and/or transformed into spherocytes. This haemolytic reaction by thrombin-activated platelets did not occur at 4 degrees C, or in the presence of agents which inhibited glycolysis or elevated intracellular levels of cAMP, indicating that energy-dependent and cAMP-regulated platelet metabolism was required for this reaction. When platelets and RBC were incubated in the same vessel, but were prevented from coming into direct cell to cell contact by means of a membrane barrier, their cytotoxicity was reduced but not eliminated completely. No cytotoxic activity against RBC was detected in platelet-free supernatants obtained by centrifugation after activation of platelets with thrombin. On the contrary, activated and washed platelets retained the activity. These observations suggested that the cytotoxic activity was carried by some diffusible and easily inactivated factors, which were continuously produced and liberated from activated platelets. Cyclo-oxygenase inhibitors inhibited the haemolytic activity of thrombin-activated platelets, suggesting a role for some products of platelet-cyclo-oxygenase pathway in platelet-mediated haemolysis. These results provide the first evidence for a direct role of activated platelets in mediation of RBC-damage in the absence of any plasma factors.

Biochemical and physiological studies of soluble esterases from Drosophila melanogaster

Twenty-two soluble esterases have been identified in D. melanogaster by combining the techniques of native polyacrylamide gel electrophoresis and isoelectric focusing. The sensitivity of each isozyme to three types of inhibitors (organophosphates, eserine sulfate, and sulfydryl reagents) identified 10 as carboxylesterases, 6 as cholinesterases, and 3 as acetylesterases. Three isozymes could not be classified and no arylesterases were identified. The carboxyl- and cholinesterases could each be further divided into two subclasses on the basis of inhibition by organophosphates and sulfhydryl reagents, respectively. Choline- and acetylesterases have characteristic substrate preferences but both subclasses of carboxylesterases are heterogeneous in substrate utilization. Subclass 2 carboxylesterases exhibit diverse temporal expression patterns, with subclass 1 carboxylesterases generally found in larvae and subclass 1 cholinesterases and acetylesterases more characteristic of pupae and adults. Tissues showing the greatest number of isozymes are larval body wall (eight) and digestive tract (six in larvae, six in adults). Carboxylesterases are distributed across a wide range of tissues, but subclass 1 cholinesterases are generally associated with neural or neurosecretory tissues and subclass 2 cholinesterases with digestive tissues.

Cellular cytotoxic function and potential in acute myelogenous leukaemia

Twenty-seven adult AML patients (13 with active disease and 14 in complete remission) were investigated for their cellular cytotoxic potential and function. All AML patients, whether with active disease or in complete remission, showed increased percentage of CD3+ lymphocytes expressing the cytotoxicity-linked cytoplasmic serine esterase, suggesting a higher than normal cytotoxic potential. However, when the cytotoxic function in these patients were analysed in terms of the natural killer and lectin-dependent cellular cytotoxicity, all AML patients, whether with active disease or in complete remission, had impaired target cell lytic activity. This paradox of cytotoxicity is most likely due to the immunosuppressive effect of the serum factor elaborated by leukaemia myeloblasts.

Effect of esterase inhibition on the disposition of zomepirac glucuronide and its covalent binding to plasma proteins in the guinea pig

The disposition of zomepirac (Z) and its acyl glucuronide metabolite were studied in rabbits and guinea pigs to determine if hydrolysis of zomepirac glucuronide (ZG) by tissue esterases occurs in vivo and what effect inhibition of esterases would have on exposure to ZG and subsequent covalent binding to plasma proteins. ZG was hydrolyzed rapidly in vivo by both guinea pigs and rabbits, liberating Z. The effect of inhibition of tissue esterases was determined by administration of phenylmethylsulfonyl fluoride (PMSF) concurrently with i.v. doses of Z or ZG to anesthetized, bile duct ligated guinea pigs. Administration of PMSF decreased the apparent plasma clearance of ZG by 86% and elevated the apparent plasma clearance of Z by 300%. Exposure of the guinea pigs to ZG as measured by the area under the plasma concentration vs. time curve (AUC) was increased substantially by PMSF treatment. Covalent binding of Z to plasma proteins in the guinea pig correlated well with AUC of ZG, but not with AUC of Z. The correlation of Z covalent binding with AUC of ZG in the guinea pig is similar to that found in humans suggesting that the degree to which acyl glucuronides form covalent adducts with proteins in humans may be predictable from studies in animals.

Influence of the organophosphorus compound DFP on inhibitory motor systems and esterase activity in the spinal cord of cats

In high spinal cats, the acute time-dependent changes of both the activity of spinal reflex pathways and the activity of three different esterases (acetylcholinesterase, carboxylesterase and neurotoxicant target enzyme) in the spinal cord were investigated after intravenous application of the organophosphorus compound di-isopropyl phosphofluoridate (DFP). There is no general depression of spinal reflexes by DFP. While the recurrent inhibition is completely abolished for a long time and the reflexes to a flexor (PBSt) are depressed but with a shorter recovery time, the reflexes to an extensor (GS) are distinctly less depressed or even facilitated. Reflex pathways from skin afferents to motoneurones did not react in a uniform way to DFP, e.g. inhibitory nociceptive pathways were less affected than excitatory ones. Esterase activities were heavily depressed and recovered with different time courses. The acute DFP action cannot be explained by a uniform intoxication of all spinal functions but probably emerges from a differential action on different interneuronal systems.

Comparative distribution of acid phosphatase and simple esterase in the mouse neocortex and hippocampal formation

The present study deals with the detailed distribution of acid phosphatase (AcP) and simple esterase (SE) in different layers of the neocortex and hippocampal formation of the mouse brain. The neurons, in general, had moderate to intense enzyme activity for AcP and mild to moderate activity for SE. The AcP activity dominated in the neuronal population as compared to the neuropil; the neuropil stained mildly for SE. The large pyramidal cells in the neocortex and cornu ammonis, and the granular cell layer of the gyrus dentatus, demonstrated strong enzyme activity both in AcP and SE preparations. The role of AcP and SE has been discussed in relation to various structures of the neocortex and hippocampal formation.

Bacteriology of the cervix in cases of infertility: effect on human and animal spermatozoa and role of elastase

Microorganisms such as Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans isolated from cervices of infertile human females inhibited motility and agglutinated human, cow bull, buffalo bull, and rat spermatozoa in vitro. Fifty percent of the infertile females studied carried elastase-positive microorganisms. Cell-free culture supernatants of 72-hr-old elastase-positive cultures were spermicidal within 60 min of contact with sperm, while elastase-negative cultures were spermicidal in 4-6 hr. Cultures of all the cervical isolates were spermicidal and agglutinated human, cow bull, buffalo bull, and rat spermatozoa, and these activities increased with age of the culture. Human sperm showed only tail-to-tail agglutination, while cow bull, buffalo bull, and rat spermatozoa showed mainly head-to-head agglutination. Spermicidal activity was also attributable to elastase, which was present more in 72-hr-old cultures than in 24-hr-old cultures.

"A" esterases and their role in regulating the toxicity of organophosphates

Esterases which can hydrolyse organophosphates without being inhibited by them are termed "A" esterases. Using paraoxon and pirimiphos-methyl oxon as substrates, high "A" esterase activity is found in the liver and plasma or serum of a range of mammalian species. In a study of serum "A" esterases of sheep and humans, over 80% of the activity separated into the high density lipoprotein (HDL) fraction following ultracentrifugation. When HDL fractions from sheep serum were run on Sepharose gel columns, most of the paraoxonase activity separated as a single peak of estimated molecular weight 360,000, which corresponds to that of HDL2 of humans. During the course of purification of "A" esterases by three different column procedures, contrasting esterase elution profiles were obtained with organophosphate and pyrethroid substrates. This was strong evidence for the existence of multiple forms of HDL "A" esterases. Levels of "A" esterase activity in plasma and liver of birds were much lower than those of mammals. This appears to be the main reason why birds are much more susceptible than mammals to organophosphates such as pirimiphos-methyl and diazinon which form active oxons that are good substrates for mammalian "A" esterases. No "A" esterase was detected in strains of rust red flour beetle (Tribolium castaneum) which were resistant to organophosphates. Similar observations have been made with strains of other insects resistant to organophosphates, raising the question to what extent esterases of this type are present in insects.