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L S Forster

Publications and source records attributed to L S Forster.

8 recordsLinked to original sources
PubMed1979

Lifetimes and NADH quenching of tryptophan fluorescence in pig heart cytoplasmic malate dehydrogenase.

The time-resolved and steady state fluorescence properties were measured for pig heart cytoplasmic malate dehydrogenase at pH 6.0 and 8.0. The fluorescence decay can be described by two rate processes, according to the functions: I(t) = 0.7e(-t/1.0) + 0.3e(-t/4.4) for the free enzyme and I(t) = 0.7e(-t/0.8) + 0.3e(-t/2.0 for the enzyme . NADH complex. Quenching by NADH of the tryptophan fluorescence is linear. The only effect of pH is to change the association constant for NADH binding; the fluorescence of the free enzyme and the fluorescence quenching by NADH, I-, and acrylamide are unaffected by pH. Thus there are no changes in conformation of the free enzyme or of the NADH complex over the range of pH 6 to 8.

Animals↗
PubMed1979

Lifetimes and NADH quenching of tryptophan fluorescence in pig heart lactate dehydrogenase.

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.

Animals↗
PubMed1976

Tryptophan fluorescence and homology in lysozymes and alpha-lactalbumins.

Steady-state and transient fluorescence properties of turkey lysozyme, human lysozyme, and bovine alpha-lactalbumin are compared to those of hen lysozyme and hen lysozyme derivatives. Tryptophan fluorescence appears to be sufficiently sensitive to environment so that a small divergence in sequence can alter the fluorescence properties of one or more of the sequentially equivalent tryptophans in these proteins. Thus, an understanding of the fluorescence of one protein cannot necessarily be extended to a homologous protein in a simple manner, and the use of fluorescence to document structural similarity in homologous proteins is likely to be difficult. In addition, the results with alpha-lactalbumin and human lysozyme suggest that multiple conformations of these proteins exist in solution, and that interconversion of these conformations is slow compared to the fluorescence lifetime.

Animals↗
PubMed1975

Optical properties of lysozyme. pH and saccharide binding difference spectra.

Difference spectra associated with changes in pH and with binding of saccharides have been recorded for hen egg white (HEW) lysozyme, turkey egg white (TEW) lysozyme, and for the derivatives of the hen protein in which Tre-62 or Trp-108 had been oxidized specifically to oxindolealanine to give the Oxa-62 or Oxa-108-proteins. Identical pH difference spectra were obtained for HEW, TEW, and Oxa-62-lysozymes. Oxidation of Trp-108 is reflected in both the high and low pH (pH 7 versus 5 and pH 2 versus 5) difference spectra. The magnitude of the low pH difference spectrum is enhanced by binding of saccharide for HEW and Oxa-62-lysozymes but not for TEW lysozyme. The shapes and magnitudes of saccharide binding difference spectra are affected by oxidation of residues 62 or 108. These results can be interpreted in terms of the perturbations responsible for the lysozyme difference spectra. The pH 7 versus 5 difference spectrum results from perturbation by Glu-35 of Trp-108 and another tryptophan, probably Trp-63. Perturbation of Trp-108 and one or more other tryptophan residues by several carboxylate groups is responsible for the low pH difference spectra of the unliganded HEW and TEW lysozyme molecules. Perturbation of Trp-108 makes a principal contribution to the saccharide-binding difference spectrum. Perturbation of the Oxa-108 chromophore by ionization of Glu-35 or by saccharide binding produces absorbance changes in the 250 to 265 nm region.

Acetylglucosamine↗
PubMed1975

The circular dichroism of lysozyme.

The circular dichroism spectra of hen egg white lysozyme, and of lysozyme derivatives in which tryptophan residues 62 or 108, or both, are selectively oxidized, have been measured as a function of pH over the range of 200 to 310 nm. Neither Trp-62 nor Trp-108 is principally responsible for the positive rotational strength in the 280 to 300 nm region. The spectrum in the 200 to 230 nm region is nearly the same in the native protein and in the derivatives, and is little affected by binding of saccharide. These results are used to reinterpret the circular dichroism spectra of the lysozymes and alpha-lactalbumins.

Amino Acid Sequence↗
PubMed1975

Tryptophan fluorescence lifetimes in lysozyme.

Tryptophan fluorescence lifetimes at pH 2 and pH 8 have been obtained for lysozyme and for lysozyme derivatives in which tryptophan-62 or tryptophan-108 or both are nonfluorescent. The lifetimes range from about 0.5 ns to 2.8 ns for the various emitting tryptophans. The tryptophan lifetimes appear to increase with exposure of tryptophan to solvent, but intramolecular contacts, probably with cystine residues, can considerably shorten the lifetime. Intertryptophanyl interactions can also affect fluorescence lifetimes. The trytophan-108 lifetime in lysozyme is shorter than in the derivative in which tryptophan-62 is oxidized; this is ascribed to energy transfer from tryptophan-108 to tryptophan-62. From the lifetime results the relative intensities emitted by specific tryptophans can be estimated, and these values also support the existence of intertryptophanyl energy transfer. The emission intensity from tryptophan-62 is greater in the presence of tryptophan-108, and the emission intensity of tryptophan-108 appears to be greater in the absence of tryptophan-62. Conformational effects accompanying chemical modification of tryptophan cannot be completely ruled out, however. The tryptophan-62 lifetime at pH 8 in lysozyme is shorter than in the derivatives, which might indicate a subtle conformational effect. Studies with tri-(N-acetyl-glucosamine)-protein complexes indicate that both the tryptophan lifetimes and the number of emitting tryptophans may be changing upon complexation. The results illustrate the usefulness and the limitations of lifetime measurements in understanding protein fluorescence.

Animals↗