Label-free continuous enzyme assays with macrocycle-fluorescent dye complexes.

We introduce a new economic, convenient and general assay principle based on the reversible interaction of water-soluble macrocycles and fluorescent dyes. We show that amino acid decarboxylase activity can be continuously monitored by measuring changes in fluorescence, which result from the competition of the enzymatic product and the dye for forming a complex with a cucurbituril or calixarene macrocycle. The new assay provides a complementary method to the use of antibodies, radioactive markers and labeled substrates.