Determination of d-aspartate N-methyltransferase activity in the starfish by direct analysis of N-methyl-d-aspartate with high-performance liquid chromatography

We describe a method for the detection and quantification of d-aspartate N-methyltransferase activity. The enzyme catalyzes the S-adenosyl-l-methionine-dependent N-methylation of d-aspartate to form N-methyl-d-aspartate (NMDA). NMDA is detected directly by high-performance liquid chromatography (HPLC) of their (+)- and/or (−)-1-(9-fluorenyl)ethyl chloroformate fluorescent derivatives. The NMDA production in the assay mixture is linearly proportional to the incubation time and the amount of tissue homogenate. Using a 10 min incubation time, the method allows detection of the enzyme activity below 10 fmol/min. It can be used to analyze kinetic behavior and to quantify the enzyme from a wide variety of organisms.