title: Lifetimes and NADH quenching of tryptophan fluorescence in pig heart lactate dehydrogenase.
abstract: The decay of tryptophan emission from pig heart lactate dehydrogenase following pulsed excitation has been recorded in Tris buffer solution at pH 7.4. All tryptophan residues emit. A good least-squares two-component fit is obtained with I(t)-0.53e-t/1.2 + 0.47e-t/68. A longer lived emitter (r=7.4--8.1 ns) is also observed. Bound NADH strongly quenches most of the 6.8-ns emission, but the 1.2-ns component is relatively unaffected. The fluorescence is moderately quenched by acrylamide and only slighty quenched by I- and Cs+. The pulsed and steady-state fluorescence is discussed in terms of a model with three lifetime classes of tryptophan, viz., 1, 4, and 8 ns. The three-dimensional structure of the enzyme--NADH complex is used to develop a description of the individual residues in terms of their lifetimes and sensitivity to NADH and I- quenching. The nonlinear NADH quenching is due to intersubunit energy transfer from Trp-248 to NADH.
mesh_terms: D000818:Animals; D007700:Kinetics; D007770:L-Lactate Dehydrogenase; D009206:Myocardium / Q000201:enzymology; D009243:NAD; D010084:Oxidation-Reduction; D013050:Spectrometry, Fluorescence; D013552:Swine; D014364:Tryptophan
chemical_list: D009243:NAD; D014364:Tryptophan; D007770:L-Lactate Dehydrogenase