240] Sensitive fluorometric and radiometric assays for monoamine oxidase and diamine oxidase

Abstract

This chapter discusses sensitive fluorometric and radiometric assays for monoamine oxidase and diamine oxidase. The fluorometric method described in chapter has been compared with radiometric assays for monoamine oxidase and diamine oxidase. Putrescine has been used as substrate for rat small intestinal diamine oxidase, and tyramine as substrate for brain monoamine oxidase. Incubation conditions for the simultaneous radiometric and fluorometric assays have been identical with respect to total volume, enzyme and substrate concentrations, and incubation times except that the radiometric assay mixtures do not contain homovanillic acid and horseradish peroxidase. Tyramine consumption by brain homogenates and putrescine consumption by small intestinal preparations is the same with fluorometric and radiometric techniques. In the radiometric assays of diamine oxidase and monoamine oxidase, the deaminated products are measured, whereas hydrogen peroxide production is assayed in the fluorometric method. Because these methods give the same results, the enzymatic formation of detectable hydrogen peroxide would appear to be stoichiometric with the formation of deaminated products.