Phenyl Valerate Research Articles

Neurotoxic esterase. Identification of two isoenzymes in hen brain.

Two phenyl valerate hydrolyzing carboxylesterases (EC 3.1.1.1) of hen brain were identified as neurotoxic esterases (NTEA and NTEB) by kinetic analysis of organophosphorus inhibition curves. The activities of both NTE isoenzymes with phenyl valerate (PV) as substrate and their inhibition rate constants were determined in six different animals. In-vivo-application of a single oral dose of 500 mg/kg triorthocresyl phosphate (TOCP) caused 86% inhibition of NTEA and 93% inhibition of NTEB within 24 h. Total NTE activity (NTEA plus NTEB) determined by kinetic analysis shows an excellent correlation (r = 0.989) to NTE activity simultaneously tested with a differential NTE assay. The excellent sensitivity (97%) and high specificity (79%) of the NTE differential test is demonstrated.

Separation of paraoxon and mipafox sensitive esterases by sucrose density gradient sedimentation

Paraoxon- and mipafox-sensitive phenyl valerate (PV) hydrolases found in chicken nervous tissue were solubilized by Triton X-100 and separated by sucrose density gradient centrifugation. Enzyme activity from chick embryo brain with properties of neurotoxic esterase (NTE, intensitive to 40 μM paraoxon, sensitive to 50 μM mipafox) migrated in a 9S peak.

Carboxylesterases in primate brain: characterization of multiple forms

1. l. Carboxylesterase activity of primate brain ( Macaco mulatta) was determined using phenyl valerate (PV) as substrate. 2. 2. Eight earboxylesterases of primate brain were characterized in respect to PV-hydrolysing activity and to their inhibition rate constants for the reaction with organophosphorus compounds. 3. 3. Carboxylesterase III was identified as neurotoxie esterase (NTE). 4. 4. Organophosphate inhibition data of primate acetylcholinesterase (EC 3.1.1.7) and of primate cholmesterase (EC 3.1.1.8) were determined and are compared to corresponding data of primate brain earboxylesterases. 5. 5. Physiological functions, clinical and toxicological significance of primate brain earboxylesterases are discussed.

Evidence for the existence of neurotoxic esterase in neural and lymphatic tissue of the adult hen

Hen brain and spinal cord contain a number of esterases that hydrolyze phenyl valerate (PV). Most of this activity is sensitive to inhibition by micromolar concentrations of paraoxon. Included among the paraoxon-resistant esterases is neurotoxic esterase (NTE), which is inhibited in vivo and in vitro by certain organophosphorus compounds, such as mipafox, which cause delayed neurotoxicity. Since published information on the NTE content of non-neural tissues was heretofore lacking, a comprehensive study was undertaken of the occurrence of this enzyme in tissues of the adult hen ( Gallus gallus domesticus), the species of choice in the study of organophosphorus-induced delayed neurotoxicity. Complete differential titration curves of PV esterase activity were obtained by preincubation of each tissue homogenate with a wide range of concentrations of paraoxon, a non-neurotoxic compound, plus or minus mipafox, a neurotoxic compound, followed by PV esterase assay. Brain NTE activity was determined to be 2426 ± 104 nmoles · min −1 · (g wet weight) −1 (mean ± S.E.M.). Titration of other tissues resulted in the following NTE activities, expressed as percentages of brain NTE activity: spinal cord (21%), peripheral nerve (1.7%), gastrocnemius muscle (0%), pectoralis muscle (0%), heart (14%), liver (0%), kidney (0%), spleen (70%), spleen lymphocytes (26%), and blood lymphocytes (24%). Using an abbreviated procedure, erythrocytes and plasma showed no NTE activity. These results indicate that NTE has limited distribution among the tissues of the adult hen and is present in lymphatic as well as neural tissue.

Gel-electrophoretic identification of hen brain neurotoxic esterase, labelled with tritiated di-isopropyl phosphorofluoridate.

The particulate fraction from hen brain was labelled with [3H]di-isopropyl phosphorofluoridate (DiPF) and separated by polyacrylamide-gel electrophoresis. Four radioactive protein bands (1--4) of molecular weights 155000, 92000, 60000, and 30000 were resolved. Most of the labelling of bands 2, 3 and 4 was inhibited by preincubation with Paraoxon. The residue in band 4 was sensitive to pH 5.2. Successive treatments with Paraoxon and pH 5.2 resulted in the abolition of bands 3 and 4. Bands 1 and 2 contained one and two polypeptides respectively, whose labelling was sensitive to Mipafox, but one, in band 2, was sensitive to higher concentrations of Paraoxon. The concentrations of the other two polypeptides were 6.7 and 1.95 pmol of DiPF bound/g of brain in bands 1 and 2 respectively. Both were as sensitive to Mipafox as neurotoxic esterase and were also sensitive to phenyl benzylcarbamate. 4-Nitrophenyl di-n-pentylphosphinate given in vivo inhibited neurotoxic esterase and the labelling of the band-1 polypeptide by 82% and 84% respectively, but inhibited the labelling of the band 2 polypeptide by 51%. The phosphinate in vitro produced 98% inhibition of the labelling of the band-1 polypeptide, with only 26% inhibition of the band-2 polypeptide, under conditions sufficient to inhibit neurotoxic esterase totally. Both neurotoxic esterase and the band-1 polypeptide were found in the forebrain at 1.74-fold their concentration in the rest of the brain, whereas the band-2 polypeptide was uniformly distributed. The evidence indicates that the Mipafox-sensitive polypeptide in band 1 is the [3H]DiPF-labelled active-site subunit of neurotoxic esterase. The catalytic-centre activity of the enzyme for phenyl valerate hydrolysis was found to be 2.6 x 10(5) min-1.

The Internal Field Parameters for Liquid Crystals

Abstract This paper presents calculations of the internal field constants γe for four homologous liquid crystal materials in their nematic and crystalline phases. We find that for the nematic phase, the γe ∼ S 2 curve is nearly a straight line for each compound. When one extrapolates the straight line to S 2 = 1, the corresponding γe value is nearly equal to γ∥, the crystalline internal field constant. The birefringence data used are those reported by Somashekar et al.4 The four compounds studied are: (1) p(p'-ethoxyphenylazo)phenyl valerate; (2) p(p'-ethoxyphenylazo)phenyl hexanote; (3) p(p'-ethoxyphenylazo)phenyl heptanoate; (4) p(p'-ethoxyphenylazo)phenyl undecylenate.

Structure-activity relationships for substrates and inhibitors of hen brain neurotoxic esterase

(1) Neurotoxic esterase is one of several paraoxon-resistant esterases of hen brain. It has previously been assayed with phenyl phenylacetate as substrate by a differential assay using Mipafox as selective inhibitor. The Mipafox-sensitive activity is a greater proportion (55 per cent) of the total when phenyl valerate is used as substrate and this activity behaves as a single enzyme according to several tests. Phenyl esters of other acids and esters of other phenols are less specific substrates and most are hydrolysed slower than phenyl valerate. (2) Neurotoxic esterase does not significantly hydrolyse peptides or amides but some hydrophobic peptides and amides are non-progr essive inhibitors. (3) Inhibition by a range of organophosphorus, carbamic and sulphur-acid esters has been investigated. (4) Neurotoxic esterase is similar to chymotrypsin and trypsin but unlike acetylcholinesterase in the pattern of inhibition by organophosphorus esters. The structure-activity relationships presented give some guidance for design of non-neurotoxic pesticides. (5) More stable and less toxic alternatives to Mipafox as a selective inhibitor of neurotoxic esterase have been found. (6) Benzenesulphonyl fluoride is a selective inhibitor of some of the Mipafox-resistant esterases. (7) All the esterases were inhibited by PCMB(0.1 mM)and by Zn 2+ (0.4 mM).

Specificity of hydrogen rearrangement in phenyl valerate fragmentation upon electron impact

Hydrogen rearrangement in phenyl valerate upon electron impact was found to be site selective (87%) from the α-position.