A fluorimetric method for the determination of tryptophan in animal tissues

Abstract

Tryptophan, tryptamine and peptides, containing N-terminal tryptophan give two highly fluorescent products on treatment with dithiothreitol and acid ninhydrin reagent 1 or 2. The first fluorescent product (product A) gives an emission at 500 nm on activation at 390 to 400 nm and is stable for 20 min. The second product (product B), which gives an emission at 530 nm on activation at 470 nm, is detectable within 1 hr after the reaction. It gives almost maximum intensity in 4 hr and is stable for at least 48 hr. Except lysine, which in equimolar amounts gives less than 1% of a product similar to product B, no other naturally occurring amino compounds give fluorescent products. A procedure is given for the determination of 0.05 to 34 nmol of tryptophan in tissue extracts. By using this procedure, rat brain was found to contain 17.56 ± 0.76 (S.E.M.) nmol/g wet wt.