title: Intrinsic tryptophan phosphorescence as a marker of conformation and oxygen diffusion in purified cytochrome oxidase.
abstract: Cytochrome oxidase exhibits phosphorescence from tryptophan in aqueous solution in the absence of oxygen. The lifetime for the resting reduced enzyme suspended in Tween-20 is around 30 ms at pH 8. The lifetime is longest between pH 7 and 8 and decreases with lowering of pH. Oxygen quenches the phosphorescence with a Stern-Volmer quenching constant of approximately 5 x 10(7) M-1.s-1 at 5 degrees C whereas cytochrome c has no effect. We interpret these results to indicate that room temperature tryptophan phosphorescence arises from tryptophan(s) in structured region(s) remote from the hemes and that the protein does not impose a significant barrier for the diffusion of oxygen.
authors.affiliation: Department of Biochemistry and Biophysics, School of Medicine, University of Pennsylvania, Philadelphia 19104.
authors.forename: S
authors.initials: S
authors.lastname: Papp
authors.forename: T E
authors.initials: TE
authors.lastname: King
authors.forename: J M
authors.initials: JM
authors.lastname: Vanderkooi
mesh_terms: D000818:Animals; D003576:Electron Transport Complex IV / Q000302:isolation & purification / Q000378:metabolism*; D006736:Horses; D006863:Hydrogen-Ion Concentration; D049449:Luminescence; D009206:Myocardium / Q000201:enzymology; D009994:Osmolar Concentration; D010100:Oxygen / Q000378:metabolism*; D011487:Protein Conformation; D014364:Tryptophan / Q000737:chemistry*
chemical_list: D014364:Tryptophan; D003576:Electron Transport Complex IV; D010100:Oxygen