Abstract
Organophosphate compounds can bind to carboxylesterase, which may lower the concentration of organophosphate pesticides at the target site enzyme, cholinesterase. It is unclear from the literature whether it is the carboxylesterase affinity for the organophosphate and/or the number of carboxylesterase molecules that is the dominant factor in determining the protective potential of carboxylesterase. The fundamental dilutions and kinetic effects of esterase enzyme are still poorly understood. This study aims to confirm and extend our current knowledge about the effects of dilutions on esterases activities in the blood for birds with respect to protecting the enzyme from organophosphate inhibition. There was significantly higher esterases activities in dilution 1 : 10 in the all blood samples from quail, duck, and chick compared to other dilutions (1 : 5, 1 : 15, 1 : 20, and 1 : 25) in all cases. Furthermore, our results also pointed to the importance of estimating different dilutions effects prior to using in birds as biomarker tools of environmental exposure. Concentration-inhibition curves were determined for the inhibitor in the presence of dilutions 1 : 5, 1 : 10, plus 1 : 15 (to stimulate carboxylesterase). Point estimates (concentrations calculated to produce 20, 50, and 80% inhibition) were compared across conditions and served as a measure of esterase-mediated detoxification. Results with well-known inhibitors (malathion) were in agreement with the literature, serving to support the use of this assay. Among the thiol-esters dilution 1 : 5 was observed to have the highest specificity constant (k cat/K m), and the K m and k cat values were 176 μM and 16,765 s−1, respectively, for S-phenyl thioacetate ester, while detected in dilution 1 : 15 was the lowest specificity constant (k cat/K m), and the K m and k cat values were 943 μM and 1154 s−1, respectively, for acetylthiocholine iodide ester.
Highlights
An esterase is a hydrolase enzyme that splits esters into an acid and an alcohol in a chemical reaction with water called hydrolysis [1, 2]
In this paper the author showed five dilutions to measure the activities of CbE and ChE in plasma, serum, and erythrocyte for quail, duck, and chick to reduce the turbidity of the blood samples and to ensure that the optical signal falls within the linear range of detection throughout the esterase enzyme activity measurement, and the enzyme dilution slows down the rate of spending of substrate, so providing an extended time window for statement of steady-state esterase enzyme kinetics [18, 30]
That the influence of known susceptibility factors such as CbE and ChE should not be generalized across this inhibitor [35]. This is the first paper that provided original data concerning an enzymological dilution characterization in the blood samples from birds used for human consumption
Summary
An esterase is a hydrolase enzyme that splits esters into an acid and an alcohol in a chemical reaction with water called hydrolysis [1, 2]. Carboxylesterase (CbE)/cholinesterase (ChE) family members are under esterase enzyme and are responsible for controlling the nerve impulse, detoxification, and various developmental functions and are a major target of pesticides and chemical warfare agents [2,3,4]. The reaction with the enzyme is the key to the considerable number of pharmacological actions possessed by OP, other biochemical properties of these compounds have recently been recognised as important [10]. Apart from the interest in OP as military weapons, the past thirty years have seen an unprecedented growth in their use as insecticides, stimulating the production of certain compounds such as malathion which are degraded by higher organisms while remaining toxic to arthropods [12].
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