Synthesis and Spectral Characterization of 5′-Phosphopyridoxyl-D,L-7-azatryptophan, a Photophysical Probe of Protein Structure and Dynamics

Abstract 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 aciduct 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.