title: Phosphorescence/microwave double-resonance spectra of tryptophan perturbed by methylmercury(II).
abstract: Amplitude-modulated phosphorescence/microwave double-resonance (AM-PMDR) spectra are reported for complexes of methylmercury(II) cation, designated CH3Hg(II), with tryptophan and glyceraldehyde-3-phosphate dehydrogenase (GPDHase; from rabbit muscle). Wavelength shifts are observed in the AM-PMDR spectra of CH3Hg(II)-tryptophan, which are obtained by microwave pumping in distinct zero-field D + E magnetic resonance transitions, demonstrating that AM-PMDR can be used to display selectively the phosphorescence spectra of structurally distinct complexes with different zero-field splittings. The AM-PMDR spectra accurately represent the phosphorescence of CH3Hg(II)-tryptophan. Binding of CH3Hg(II) to a cysteine site of GDPHase perturbs the luminescence of one of the two optically resolved tryptophan. The AM-PMDR spectrum of the perturbed tryptophan is obtained by microwave pumping of the D + E magnetic resonance signal, which can be observed optically only in the presence of a heavy atom perturbation. The resulting spectrum is broadened and shifted to the blue relative to the corresponding tryptophan phosphorescence spectrum of the uncomplexed enzyme. Comparison of the AM-PMDR spectra of CH3Hg(II)-tryptophan and CH3Hg(II)-GPDHase suggests that there are differences in the mechanisms of heavy atom perturbation in these complexes.
mesh_terms: D000818:Animals; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000032:analysis; D008163:Luminescent Measurements; D008767:Methylmercury Compounds; D008872:Microwaves; D009132:Muscles / Q000201:enzymology; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D013057:Spectrum Analysis; D014364:Tryptophan / Q000032:analysis*
chemical_list: D008767:Methylmercury Compounds; D014364:Tryptophan; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases