文摘
We have obtained low-temperature magnetic circular dichroism (MCD) spectra for ferric cyano complexes of the wild type and E546N mutant of a human inducible nitric oxide synthase (iNOS) oxygenase/flavin mononucleotide (oxyFMN) construct. The mutation at the FMN domain has previously been shown to modulate the MCD spectra of the l-arginine-bound ferric iNOS heme (Sempombe, J.; et al. J. Am. Chem. Soc.2009, 131, 6940鈥?941). The addition of l-arginine to the wild-type protein causes notable changes in the CN鈥?/sup>-adduct MCD spectrum, while the E546N mutant spectrum is not perturbed. Moreover, the MCD spectral perturbation observed with l-arginine is absent in the CN鈥?/sup> complexes incubated with N-hydroxy-l-arginine, which is the substrate for the second step of NOS catalysis. These results indicate that interdomain FMN鈥揾eme interactions exert a long-range effect on key heme axial ligand鈥搒ubstrate interactions that determine substrate oxidation pathways of NOS.
