engleski

Optimization of PON1 arylesterase activity measurement

Paraoxonase (PON1) prevents the oxidation of low density lipoproteins (LDL) and is associated with the risk of developing atherosclerosis, cardiovascular disease and myocardial infarction. The reduced catalytic activity of PON1 in humans has been demonstrated in many pathological conditions such as diabetes, chronic kidney or liver disease, hyperlipoproteinemia, Alzheimer's disease and thyroid diseases. Mammalian PON1 possesses arylesterase, lactonase and phosphotriestrase activity. However, the physiological substrate and role of PON1 in mammals are yet to be determined. Because of its ability to hydrolyse a very broad spectrum of esters, PON1 is involved in the metabolism of many xenobiotics, some endogenous proantibiotics and lactones. The affinity of PON1 toward certain compounds cannot be determined by direct assays, but can be determined through its impact on PON1 arylesterase, paraoxonase or lactonase activity. For some esters used in the environment, such as carbamate pesticides or carbamate drugs, it is difficult to determine the impact on PON1 esterase activity. To be more precise, most of these carbamates have a maximum absorption within UV range, as does phenylacetate, a substrate commonly used to measure PON1 arylesterase activity. Within this study, the aryl esters p-nitrophenyl acetate (PNPA) and S-phenylthioacetate (PTA) were taken as substrates for measuring the arylesterase activity of recombinant PON1-G2E6 variant, since both esters have an absorption maximum in the visible area. The relation between PTA’s and PNPA’s Vm and Km constants indicated PTA as a good substitute for phenylacetate in arylesterase activity determination, yielding a similar ratio of these two constants. Optimization of PON1 lactonase activity measurements was further done with regard to measurement conditions, pH value and temperature, where measurements at pH 8.0 and 25 °C were chosen as optimal. Acknowledgment: This work was supported by the Croatian Science Foundation (Grant No. 4307), the Slovenian Research Agency (Grant No.P1-170) and Croatian-Slovenian bilateral project 2016-2017.

human PON1 ; aryl esters

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