A novel fluorometric ultramicro determination of serum leucine aminopeptidase using a coumarine derivative

A simple and rapid rate assay of serum leucine aminopeptidase is described, using a novel fluorogenic substrate, 7-L-leucyl-4-methylcoumarinylamide. The reaction is initiated by adding 10 microliter of serum, and the fluorescence development for 1 min due to the 7-amino-4-methylcoumarin liberated at 37 degrees C is followed directly on a recorder. The proposed method is proved to be free from error due to the adsorption of the substrate dye to serum albumin and to be applicable to hyperbilirubinemic sera by simple correction. The values obtained by this method showed good correlation with those obtained by the conventional method of Goldbarg and Rutenberg (Goldbarg, J.A. and Rutenberg, A.M. (1958) Cancer 11, 283-291).