Phosphorescence properties and protein structure surrounding tryptophan residues in yeast, pig, and rabbit glyceraldehyde-3-phosphate dehydrogenase

An investigation of the phosphorescence emission properties of tryptophan (Trp) was carried out in glyceraldehyde-3-phosphate dehydrogenase from yeast and from pig and rabbit muscle. Aided by the external heavy-atom effect of iodide, the dependence on excitation wavelength, and thermal quenching profiles, it was established that the 0,0 vibronic band peaked at 406 nm in the pig and rabbit proteins is made up of overlapping contributions from two Trp residues. In contrast to a previous report [Davis, J.M., & Maki, A.H. (1984) Biochemistry 23, 6249-6256], this implies that even in the muscle enzymes all three aromatic side chains are phosphorescent. Further, when the nature of the local environment of each residue is compared to the crystallographic structure of lobster GPDH, it leads to a complete new assignment of the individual phosphorescence spectra. With each protein, a single Trp, identified as Trp-310, was found to display long-lived phosphorescence at room temperature. The decay of this emission gives evidence of conformational homogeneity among the subunits of the tetrameric molecule.