Proton NMR studies of noncovalent complexes of cytochrome c peroxidase-cyanide with horse and yeast ferricytochromes c

Noncovalent complexes of cyanide-ligated cytochrome c peroxidase with horse ferricytochrome c and yeast isozyme-1 ferricytochrome c have been formed in 10 mM potassium nitrate salt solutions and studied by proton NMR spectroscopy. The chemical shifts in the ferricytochrome c spectrum induced by complex formation with low-spin, cyanide-ligated cytochrome c peroxidase are similar to the corresponding shifts induced by complex formation with resting-state cytochrome c peroxidase, found previously. As with the resting-state enzyme, the complex between yeast cytochrome c and cytochrome c peroxidase-cyanide exhibits the larger set of complex-induced shifts. Two-dimensional proton NMR spectroscopy has been used to make resonance assignments. This was necessitated due to the extensive resonance overlap between the two proteins in the hyperfine shift region, since both heme proteins in this complex are low-spin paramagnetic species. These results expand preliminary work that revealed for the first time that cytochrome c binding affected the resonances of protons in the peroxidase heme pocket [Yi, Q., Erman, J. E., & Satterlee, J. D. (1992) J. Am. Chem. Soc. 114, 7907-7909]. The pattern of cytochrome c peroxidase complex-induced shifts is largely consistent with the X-ray crystal structures of these two complexes that have recently been published.