Triplet state of tryptophan in proteins: the nature of the optically detected magnetic resonance lines

Abstract

Optical detection of magnetic resonance (ODMR) was employed to examine the homogeneity of the tryptophan environment, both of the isolated residue in solvent and of tryptophan in glucagon and lysozyme and azurin B (Pseudomonas aeruginosa). From the shifts in the zero-field splittings, tryptophan in lysozyme, azurin or glucagon does not have the same type of solvent interaction as the free residue. However, by burning holes in the ODMR lines, it is evident that the lines in these cases are inhomogeneously broadened. From the relative line widths and hole widths, it appears that ODMR can be used to examine the relative diversity of interactions for a luminescent amino acid in a protein. The ODMR line characteristics are followed in a progression from free N-acetyl-L-tryptophanamide, to tryptophan in lysozyme, to denatured lysozyme. The line widths narrow as the tryptophan residues become less solvent accessible.