A specific method for determination of free tryptophan and endogenous tryptophan in Escherichia coli.

A sensitive, simple spectrofluorometric technique for determination of tryptophan inamounts as small as 10 pmol is described. It is based on tryptophanase hydrolysis of tryptophan and spectrofluorometric analysis of the resulting indole. The relationship between released indole and fluorescence is linear over three orders of magnitude. The method is free from interference by other amino acids, polar indole derivatives, and a number of other compounds found in cell extracts or used in bacterial growth media. The method is rapid, reproducible, and accurate. A simple method for extraction and measurement of endogenous free tryptophan from bacterial cells is also described.