Biotinylated indoles as probes for indole-binding proteins

Biotinylated indoles were prepared for application as bifunctional probes f or the detection of indole-binding proteins which participate in the life p rocesses of humans, animals, plants, and bacteria. The indole nucleus was f unctionalized, at ring positions 3, 5, or 6, by attachment of a 2-aminoethy l group, which was then coupled to the carboxyl moiety of biotin, via a spa cer composed of 3 or 4 concatenated beta -alanine residues. The constructs thus obtained were able to inhibit tryptophanase activity, similarly to ind ole in a concentration-dependent manner. They also bound strongly to lysozy me and weakly to bovine and human serum albumins, in accordance with the kn own affinities of these proteins for indole and 3-(2-aminoethyl)indole (try ptamine). The biotin end of the protein-bound bifunctional probes could the n be detected by coupling to (strept)avidin conjugated to alkaline phosphat ase or horseradish peroxidase, followed by incubation with substrates which are converted by these enzymes to intensely colored or chemiluminescent pr oducts.