A New Rapid and Sensitive Bioluminescence Assay for Monoamine Oxidase Activity

The in vivo luminescence of an aldehyde-requiring mutant of the luminous bacteria Vibrio harveyi (M42) increases dramatically upon the addition of long-chain aliphatic aldehydes (C8-C16). The intensity of this luminescence is linearly related to aldehyde concentration. This property was utilized for the determination of monoamine oxidase activity using n-octylamine and n-decylamine as substrates, which are converted by monoamine oxidase to n-octylaldehyde and n-decylaldehyde, respectively. The addition of the amine to a suspension containing rat liver mitochondria and M42 cells initiated a luminescence that was directly proportional to monoamine oxidase activity according to two parameters: (1) the rate of the initial increase in luminescence and (2) the final "steady-state" level of luminescence. The new assay has advantages of high sensitivity, rapidity, the possibility to perform discontinuous as well as continuous monitoring of monoamine oxidase activity, and applicability to turbid preparations.