Magnetic and natural circular dichroism of L-tryptophan 2,3-dioxygenases and indoleamine 2,3-dioxygenase. II. Spectra of their ferric cyanide and ferrous carbon monoxide complexes and an oxygenated form.

Both ferric cyanide and ferrous CO complexes of Ltryptophan 2,3-dioxygenases and an indoleamine 2,3dioxygenase showed magnetic CD spectra similar to those of corresponding low spin complexes of myoglobin.However, intensities of their Soret magnetic CD were often unusually high as compared to those of other hemoproteins such as myoglobin and horseradish peroxidase.Upon addition of L-tryptophan, the high intensities decreased to an ordinary level, indicating that the substrate binding affects the electronic configuration of these low spin complexes.On the basis of these findings, we suggest that both the Fe-C-N and the Fe-C-0 bonds, which are rather close to a linear configuration in the absence of L-tryptophan, became bent upon binding with the substrate.An oxygen complex of ferrous indoleamine 2,3-dioxygenase in the absence of L-tryptophan showed a magnetic CD spectrum analogous to those of oxymyoglobin and compound I11 of horseradish peroxidase.In the CD spectra, both cyanide and CO complexes of L-tryptophan 2,3-dioxygenases exhibited a strong negative extremum in the Soret region.Their intensities were not significantly affected by the addition of Ltryptophan except for a CO complex of the rat liver enzyme.On the other hand, CO and cyanide complexes of indoleamine 2,3-dioxygenase showed a couple of weak extrema which were converted to a single distinct negative extremum upon addition of L-tryptophan.These changes in natural CD spectra are discussed in terms of the interaction between the heme and nearby aromatic amino acid residue(s) in the heme pocket.