PROTON NMR-STUDY OF A NONCOVALENT COMPLEX FORMED BETWEEN CYTOCHROME-C PEROXIDASE-CYANIDE AND TUNA FERRICYTOCHROME-C

A non-covalent complier of cyanide-ligated cytochrome c peroxidase (CcPCN) with tuna ferricytochrome c, formed in low-concentration KNO3 solutions, was studied by proton NMR spectroscopy. Complex formation affects the ferricytochrome c spectrum similarly to the spectral changes previously observed for the corresponding complex formed using resting state cytochrome c peroxidase. The CcPCN-tuna ferricytochrome c complex studied here is also similar to the previously studied CcPCN complexes with both horse and yeast iso-1 ferricytochromes c. For this complex both proteins are in the low-spin iron(III) form, which make them both paramagnetic and causes severe overlap in the proton hyperfine resonance shift region. Two-dimensional proton NMR spectroscopy has been used to resolve this overlap and make proton resonance assignments. These results complete the set of experiments carried out on the complexes of CcPCN with three species of ferricytochrome c (bores, yeast and tuna) and reveal that as for the similar complexes of these ferricytochromes c with the resting-state, high-spin form of the peroxidase, the tuna results closely follow those of the horse ferricytochrome c complex. These results also extend preliminary work that revealed for the first time that cytochrome c binding was reflected in hyperfine resonance shifts of protons in the peroxidase heme pocket.