Potentiometric Determination of Arylsulfatase Activity Using a Novel Nitrocatechol Sulfate PVC Membrane Sensor

A novel potentiometric assay method for arylsulfatase enzyme is described based on measuring the initial reaction rate of hydrolysis of 4-nitrocatechol sulfate (4-NCS) substrate under optimized conditions. A monitoring sensor incorporating a PVC membrane with a nickel(II) bathophenanthroline-4-NCS ion-pair complex as electroactive material and 2-nitrophenyl phenyl ether as solvent mediator is developed and characterized. The sensor exhibits fast and stable linear response for 8 × 10^-3-7.5 × 10^-67M 4-NCS with an anionic slope of 58.5 ± 0.2 mV/decade over the pH range 3-6. The sensor is used to follow up the decrease in a fixed concentration of 4-NCS (2 × 10^-4M) as a function of arylsulfatase activity at pH 5.6 and 37 °C. A linear relationship between the initial rate of substrate hydrolysis and enzyme activity holds for 0.2-2.4 IU/mL (SD 2%). Activity measurement of arylsulfatase enzyme isolated from camel liver gives results that compare favorably well with data obtained using the standard spectrophotometric assay method. Significant advantages over many of the previously described spectroscopic methods are offered by the proposed potentiometric technique.