Long-lived tryptophan fluorescence in phosphoglycerate mutase.
Phosphoglycerate mutase (PGM; EC 2.7.5.3) isolated from rat and rabbit muscle has been shown to possess an unusually long-lived fluorescence component when excited by ultraviolet light below 310 nm. On the basis of spectral and physical measurements, this 16.4 (+/- 0.2) ns fluorescence lifetime at room temperature is assigned to a tryptophan residue in an unusual environment. The emission profile of this long-lived tryptophan is red shifted from the other tryptophans of PGM by approximately 25 nm. PGM has been crystallized and sequenced from yeast where it has been shown to be a tetramer with 29K subunits. However, we have not been able to detect the existence of an unusually long-lived fluorescence component in the yeast isomer. The long fluorescence lifetime is lost upon denaturation of rabbit PGM and is partially restored upon introduction of the protein to a nondenaturing environment, suggesting the long lifetime is not the result of a covalent modification. The PGM molecule was studied by a number of techniques including time-resolved tryptophan fluorescence, quenching studies of tryptophan fluorescence, and enzyme activity studies. The long-lived fluorescence has been shown to be statistically quenched by Br-, I-, and Cu2+ in the submillimolar region while the acrylamide quenching shows the tryptophan is marginally accessible to solvent. Characterization of the long-lived fluorescence and its possible sources are discussed.
Schauerte
J A
JA
Institute of Gerontology, University of Michigan, Ann Arbor 48109.
Gafni
A
A
D000818:Animals; D007700:Kinetics; D010736:Phosphoglycerate Mutase / Q000378:metabolism*; D010770:Phosphotransferases / Q000378:metabolism*; D011487:Protein Conformation; D011489:Protein Denaturation; D011817:Rabbits; D013050:Spectrometry, Fluorescence / Q000379:methods; D013816:Thermodynamics; D014364:Tryptophan
D014364:Tryptophan; D010770:Phosphotransferases; D010736:Phosphoglycerate Mutase