Cutinase inhibition by means of insecticidal organophosphates and carbamates

Prolonged postdiapause: influence on some indicators of carbohydrate and lipid metabolism of the red mason bee, Osmia rufa

Bees of the genus Osmia are being used in crop pollination at an increasing rate. However, a short life expectancy of adult individuals limits the feasibility of their use. Cocoons of the red mason bee, Osmia rufa L. (Hymenoptera: Megachilidae), can be stored at 4° C in a postdiapause state, and adult bees can be used for pollination outside their natural flight period. The period of storage in this form has an unfavorable influence on the survival rate, life expectancy, and fertility of the bee. It was suggested that the negative results are connected with exhaustion of energy reserves. To test this hypothesis, the present study examined the contents of protein, carbohydrates, lipids, and the activities of some enzymes, and their degradation in red mason bees that emerged in spring according to their biological clock and in summer after elongated diapause. It was found that postdiapause artificially elongated by 3 months caused significant decreases in body weight, total sugar, glycogen, lipids, and protein content in O. rufa. Glucose level was highest in bees that emerged in the summer, which was coincident with increased activities of maltase and trehalase. The activities of sucrase and cellobiase were not changed, while amylase activity was considerably decreased. The activities of triacylglycerols lipase and C2, C4, C10 carboxylesterases were highest in bees that emerged in July. Low temperatures restrict O. rufa emergence, and during prolonged postdiapause, metabolic processes lead to significant reductions of structural and energetic compounds.

Immobilization of rat brain acetylcholinesterase on porous gold-nanoparticle-CaCO₃ hybrid material modified Au electrode for detection of organophosphorous insecticides

An acetylcholinesterase (AChE) purified from rat brain was immobilized onto gold nanoparticles (AuNPs) assembled on the surface of porous calcium carbonate (CaCO(3)) microsphere. The resulting AChE-AuNPs-CaCO(3) bioconjugate was mounted on the surface of Au electrode with the help of silica sol-gel matrix to prepare the working electrode. This electrode was connected to Ag/AgCl (3M/saturated KCl) as standard and Pt wire as an auxiliary electrode through a potentiostat to construct an organophosphorus (OP) biosensor. The biosensor was based on inhibition of AChE by OP compounds/insecticides. The biosensor showed optimum response at pH 7.0, 30°C, when polarized at +0.2V. Two OP compounds, malathion and chlorpyrifos could be detected in the range of 0.1-100 nM and 0.1-70 nM, respectively at 2.0-3.0% inhibition level of AChE. The sensor was reactivated by immersing it in 0.1 mM 2-pyridine aldoxime for 10 min. The detection limit of the sensor was 0.1 nM for both malathion and chlorpyrifos. The biosensor exhibited good reusability (50 times without considerable loss) and storage stability (50% within 60 days, when stored at 4°C).

Analysis of phosphorothionate pesticides using a chloroperoxidase pretreatment and acetylcholinesterase biosensor detection

Acetylcholinesterase (AChE) is responsible for the hydrolysis of acetylcholine in the nervous system. It is inhibited by organophosphate and carbamate pesticides. However, this enzyme is only slightly inhibited by organophosphorothionates, which makes the detection of these pesticides analytically very difficult. A new enzymatic method for the activation and detection of phosphorothionates was developed with the capability to be used directly in food samples without the need of laborious solvent extraction steps. Chloroperoxidase (CPO) from Caldariomyces fumago was combined with tert-butyl hydroperoxide and two halides. Chlorpyrifos and triazophos were completely oxidized. Fenitrothion, methidathion and parathion methyl showed conversion rates between 54 and 61%. Furthermore, the oxidized solution was submitted to an AChE biosensor assay. Chlorpyrifos spiked in organic orange juice was oxidized, where its oxon product was detected in concentrations down to 5 microg/L (final concentration food sample: 25 microg/L). The complete duration of the method takes about 2 h.

Cutinase-like proteins of Mycobacterium tuberculosis: characterization of their variable enzymatic functions and active site identification

Discovery and characterization of novel secreted enzymes of Mycobacterium tuberculosis are important for understanding the pathogenesis of one of the most important human bacterial pathogens. The proteome of M. tuberculosis contains over 400 potentially secreted proteins, the majority of which are uncharacterized. A family of seven cutinase-like proteins (CULPs) was identified by bioinformatic analysis, expressed and purified from Escherichia coli, and characterized in terms of their enzymatic activities. These studies revealed a functional diversity of enzyme classes based on differential preferences for substrate chain length. One member, Culp1, exhibited strong esterase activity, 40-fold higher than that of Culp6, which had strong activity as a lipase. Another, Culp4, performed moderately as an esterase and weakly as a lipase. Culp6 lipase activity was optimal above pH 7.0, and fully maintained to pH 8.5. None of the CULP members exhibited cutinase activity. Site-directed mutagenesis of each residue of the putative catalytic triad in Culp6 confirmed that each was essential for activity toward all fatty acid chain lengths of nitrophenyl esters and lipolytic function. Culp1 and Culp2 were present only in culture supernatants of M. tuberculosis, while Culp6, which is putatively essential for mycobacterial growth, was retained in the cell wall, suggesting the proteins play distinct roles in mycobacterial biology.

Multienzyme inhibition assay for residue analysis of insecticidal organophosphates and carbamates

A recently developed spectrophotometric assay for the detection of organophosphorus and carbamate insecticides by means of cutinase inhibition has been successfully extended to two esterases derived from Bacillus subtilis (BS2) and rabbit liver. These esterases were selected because of their high sensitivity to the examined insecticide classes and their pronounced inhibition profile. With inhibition constants (ki) of 2.0x10(7) and 2.6x10(6) L/(mol.min) for rabbit liver esterase and BS2, respectively, chlorpyrifos oxon proved to be the strongest inhibitor directly followed by paraoxon. As compared to choline esterases and the recently studied cutinase, both esterases are surprisingly strongly inhibited by organophosphorus thions, showing k i in the range of 5.3x10(2) to 2.3x10(4) L/(mol.min). All tested insecticidal carbamates were also inhibitors of BS2 and rabbit liver esterase, albeit in a rather uniform manner. Generally, both enzymes were found to be about 2 orders of magnitude more sensitive on the studied insecticides than cutinase even with an enhanced sensitivity against plant matrix effects. Plant extracts, obtained according to the QuEChERS method, were subjected to solid-phase extraction (SPE) using a mixed mode strong anion exchanger/primary secondary amine sorbent and C18endcapped cartridges for superior cleanup. With spiked samples of apple juice, best recoveries of 73% (+/-61%), 94% (+/-25%), and 134% (+/-17%) were obtained for chlorpyrifos, parathion-methyl, and paraoxon, respectively. Results of exemplarily performed liquid chromatography-mass spectrometry control measurements were well in accordance with measurements obtained by enzyme inhibition.

Cutinase inhibition by means of insecticidal organophosphates and carbamates. 3. Oxidation of phosphorothionates by chloroperoxidase from Caldariomyces fumago

Chloroperoxidase (CPO) from Caldariomyces fumago combined with hydrogen peroxide and chloride proved to be most efficient for the transformation of organophosphorothionate pesticides, i.e., chlorpyrifos, chlorpyrifos-methyl, parathion, and parathion-methyl, into their more potent serine esterase inhibiting oxon analogues. Following CPO pre-oxidation steps, the detection limit of a recently described spectrophotometric cutinase assay could be increased by about 2 orders of magnitude as a consequence of increased inhibition rates of the organophosphates. This type of enzymatic oxidation is easier to perform and more efficient, as compared to bromine or N-bromosuccinimide, used for acetylcholine esterase (AChE) assay in water analyses, but is insufficient for complex matrices such as plant sample extracts. The performance of a complete assay, including sample preparation, oxidation, and inhibition, takes about 3 h. Performing oxidations of organophosphorus compounds, two significant anomalies were observed. Upon CPO oxidation, chlorpyrifos-methyl showed a very strong cutinase inhibition as compared to the corresponding oxon standard, and oxidized malathion, contrarily to malaoxon, revealed cutinase inhibition, which however obeyed a reversible reaction mechanism in contrast to the usually irreversible reactions of organophosphates. Except for methomyl, no significant effects of CPO oxidation on the inhibition strength of insecticidal carbamates could be detected. The applicability of the assay was tested with fruit samples spiked with chlorpyrifos at 0.2-0.5 mg/kg, thereby regarding the role of the latter as the pesticide detected most often in fruits. Mean recoveries ranged between 30-50%. An enhanced recovery of 84% was obtained for an apple juice sample spiked with parathion-methyl (0.5 mg/L).