Tryptophan residues in native and reoxidized muramidase: Luminescence properties

Abstract

The luminiscence properties of tryptophan chromophores in muramidase are affected by changes in enzyme conformation.

Fluorimetric measurements indicated that the emission spectrum of native muramidase (λ_max. = 337 mμ) was shifted toward longer wavelengths (λ_max. = 350 mμ) as a result of structural changes produced by disruption and carboxymethylation of disulfide bonds. When the disulfide bonds were reformed at pH 8, the emission spectra of reoxidized muramidase resemble that of native muramidase with regard to both general structure and band position.

The phosphorescence spectra of the muramidase species revealed the predominant contribution of tryptophan chromophores to the long-lived emission, and this observation was substantiated by decay-time measurements.

The τ_p values of native and reoxidized muramidases (τ_p = 1−1.9 sec) were remarkably shorter than the τ_p value of reduced carboxymethylated muramidase (τ_p = 4.1 sec). The possible significance of these phosphorescence and fluorescence studies are discussed.