Triplet-State Electron Spin Resonance of the Aromatic Amino Acids and Proteins

Abstract

Electron spin resonancespectra have been observed in irradiated glassy solutions of the aromatic amino acids and related molecules. The zero‐field splitting parameters of the amino acids (in cm−1) were found to be: tryptophan, D = 0.0984, E = 0.0410 ; tyrosine, D = 0.1301, E = 0.0558 ; tyrosinate ion, D = 0.1080, E = 0.0540 ; phenylalanine, D = 0.1475, E = 0.0439 . The technique of magnetophotoselection was applied to determine the relative orientations between the principal magnetic axes and the first two electronic transition moments of tryptophan, tyrosine, and the tyrosinate ion. The Δm = 2 signals associated with tyrosine and tryptophan have been observed in a number of irradiated frozen proteinsolutions. In the case of ovalbumin the Δm = 1 spectrum of the tryptophan residues was observed. In every case, the protein triplet signals appeared to be identical to those of the free amino acids.