Electronic spectroscopy and deuteration kinetics of tyrosine and tryptophan residues: an application to the study of erabutoxin b.

Abstract

The fluorescence increase on the deuterium oxide addition to the solvent medium was studied in various tryptophan- (or indole-) and/or tyrosine-containing model compounds. It was shown how the rates of the deuteration at the indole NH group of tryptophan and at the OH group of tyrosine could be followed independently of each other. The method was applied to a study of erabutoxin b molecule, a neurotoxic protein from a sea snake, to analyze the microenvironments of its single tryptophan and tyrosine residues. It was shown that the "functionally invariant" single tryptophan residue was exposed to the solvent in the surface of the molecule and that the "structurally conserved" single tyrosine residue was buried in the molecule. The rate of deuteration of the tyrosine residue (80 s(-1) at pH 6.3 and 33 degrees C) was 1/20 of that of an exposed tyrosine. It was also found that the amino group of Lys-27 quenched the fluorescence of Trp-29 but its deuteration had no effect on the fluorescence.