Three exponential fluorescence decay of horse liver alcohol dehydrogenase revealed by iodide quenching.

Abstract

Abstract— The time resolved fluorescence decay of horse liver alcohol dehydrogenase was measured using a frequency doubled picosecond dye laser and time‐correlated single‐photon counting detection. A flow‐cell technique is described which eliminates the photodegradation artifacts which commonly occur with laser excitation. A procedure is introduced which uses fluorescence quenching to reveal minor fluorescence lifetime components. The decay of the unquenched tryptophanyl fluorescence could be described by a double exponential decay law, but experiments conducted in the presence of iodide ion showed that the fluorescence decay must be more complex than this. A model is presented in which the fluorescence decay consists of three exponential components, only two of which are susceptible to quenching by iodide ion. Several possibilities are presented for the origin of this minor decay component, the most reasonable of which is that it arises from conformational heterogeneity in the solvent‐exposed tryptophanyl residue.