Synthesis and spectral characterization of 5'-phosphopyridoxyl-D,L-7-azatryptophan, a photophysical probe of protein structure and dynamics.

We report the first isolation of a unique adduct of pyridoxal 5'-phosphate, 5'-phosphopyridoxyl-D,L-7-azatryptophan, and suggest a new and easier route for synthesis and purification of 5'-phosphopyridoxyl-L-(or -D-)tryptophan. The absorbance and emission spectra of the 7-azatryptophan adduct are distinctly different than those of pyridoxal 5'-phosphate or the tryptophan adduct. We propose that 5'-phosphopyridoxyl-D,L-7-azatryptophan has great potential as an intrinsic probe in optical studies of protein dynamics.