Hydrogen Peroxide Assay for Amine Oxidase Activity

Amine oxidase activity can be assessed by measuring the conversion of substrate to product, or by measuring the formation of concomitantly formed hydrogen peroxide. Fluorometry offers greater sensitivity and selectivity than conventional calorimetric methods for measuring hydrogen peroxide, for example those based on coupled oxidation of chromogenic compounds with peroxidase, such as o -dianisidine (1 –4 ) or indigo disulfonate (5 ). The o -dianisidine method is not specific, is sensitive to superoxide radicals (6 ), and o -dianisidine may also act as an inhibitor of enzyme activity (7 ). The fluorometric method permits the use of a variety of substrates and continuous monitoring of the enzyme reaction, which are important for kinetic studies. Radiometric methods are limited by the available substrates and the measurement of product formation at a single time-point. Measurement of oxygen consumption, either manometrically or using a Clark electrode (polargraphic method), allow the use of multiple substrates, but are relatively insensitive and technically difficult. Coupled ammonia measurements are also relatively insensitive (8 ) and limited to amine oxidases acting at the primary amino groups. The method described in this chapter is comparable in sensitivity to the radiometric methods (9 ,10 ) and is relatively simple to perform.