A rapid and sensitive assay for monoamine oxidase activity

Based on the Berthelot reaction, a new sensitive and rapid procedure for monoamine oxidase (MAO) determination with substrate tyramine has been developed. The saturation with oxygen and the separation of ammonia from the substrate were omitted. At the end of incubation the samples were deproteinized with ethanol and consecutive centrifugation. The newly-formed ammonia is converted into the coloured compound indophenol, using the procedure of Fenton (1962). The indophenol concentration, respectively NH3 is determined by spectrophotometry at 625 nm, and calculated by comparison with a set of standard amounts of NH3. The enzyme activity is expressed as nanomoles ammonia, formed by 1 mg protein for 1 min. The method was tested for studying the relationship between the enzyme activity, time of incubation and protein concentration, as well as the effect of pargyline. The kinetics of MAO, using both liver and brain mitochondria as enzyme material was also studied. Considering the specificity, simplicity, versatility and rapid performance, the new method showed several advantages in comparison with the other known methods for MAO determination.