The assay of arylesterase in serum using two new colorimetric substrates, ω-nitrostyrylacetate and propionate

Abstract

1. (1) The synthesis of 4-acetoxy-3-methoxy-ω-nitrostyrene and 4-propionyloxy-3-methoxy-ω-nitrostyrene as substrates for the assay of arylesterase activity is described. These substrates are stable when stored in the dark for at least one year. 2. (2) Serum isolated from normal males and females aged between 25 and 35 years was used as a source of esterase activity. 3. (3) The chromophore (4-hydroxy-3-methoxy-ω-nitrostyrene) absorbs at 505 nm and has a molar extinction coefficient of 26800 in sodium carbonate/bicarbonate buffer, pH 9.5. 4. (4) Both acetate and propionate substrates are more soluble in aqueous alcohol than in water or buffer alone and the substrates were therefore prepared in 10% methanol. Since some non-enzymic hydrolysis occurs at 37°C, assays were carried out at 30° C. Details of both single point and reaction rate assay procedures are described. 5. (5) The properties of the arylesterases were determined in human serum using the single point and reaction rate assays. The data are similar to those previously described for these esterases using well-established procedures. 6. (6) The assays described using the ω-nitrostyryl acetate and propionate substrates are simple to perform and can be readily adapted for use in the clinical chemistry laboratory. Large numbers of samples can be rapidly assayed with the minimum number of manipulative steps.