Noninvolvement of Copper in the l-Tryptophan 2,3-Dioxygenase Reaction

Abstract l-Tryptophan 2,3-dioxygenase, a hemoprotein, purified to near homogeneity from cells of Pseudomonas fluorescens, has been shown to contain only trace amounts of copper. During the purification procedure, the heme content of the enzyme preparation increased in parallel with the specific catalytic activity, whereas that of copper decreased. The level of copper present in the highly purified enzyme preparations was about one-tenth that of the heme, indicating that the copper found was adventitious. The inhibitory effect of copper-chelating agents such as sodium diethyldithiocarbamate and bathocuproine sulfonate on the enzyme activity was not due to their specific chelating action but was attributable to their unforeseen properties as a hydrogen peroxidetrapping reagent and a nonspecific inhibitor, respectively. The results are thus incompatible with the view that l-tryptophan 2,3-dioxygenase is a copper-hemoprotein.