Evaluation of a new substrate for measurement of serum PON arylesterase activity

It was found that the hydrolysis of 9-(4-chlorophenyloxycarbonyl)-10-methylacridinium triflate (CPOCMA) could be catalyzed by recombinant human PON1. Based on this property, the CPOCMA was evaluated as a substrate for serum PON activity assay. The apparent Km value of a serum sample for the substrate was determined as 85 nmol/L, close to the Km value (83 nmol/L) of rHuPON1. The interferences by other esterase such as acetylcholinerase and lipases were investigated. The NaCl and CaCl2 as PON activity enhancers were able to improve the specific signal, respectively. The rHuPON1 in presence of CaCl2 showed at least 7.8 times selectivity over acetylcholinerase and lipases. By comparing with the UV methods based on phenyl acetate and diazinon, respectively, the proposed chemiluminescent method was validated with 30 serum samples. The method based on CPOCMA allows reliable, cost-saving, and specific determination in a buffer of physiological pH.