Can Heme Modes be Influenced By Protons?

Nuclear Resonance Vibrational Spectroscopy (NRVS) –also called Nuclear Inelastic Scattering (NIS) - is a synchrotron based technique which uses a Mössbauer active nucleus -in most cases ⁵⁷Fe- to characterize iron-ligand vibrations. This method does not depend on optical selection rules; any vibrational mode involving movement of the ⁵⁷Fe is NIS-active and therefore this technique is complementary to other methods including IR or Raman spectroscopy. In order to explore iron ligand vibrations in heme systems we have investigated the vibrational properties of Fe(III) containing model hemes as well as the NO-adducts of the NO-transporter proteins nitrophorin 2 (NP2) [1,2] and nitrophorin 7 (NP7) [3]. Theoretical QM/MM-calculations have been performed to understand and assign all iron-related vibrational modes in the range starting from 20 cm^-1 up to 600 cm^-1. Interestingly the QM/MM-calculations do also show that protonation of the heme carboxylates significantly influences the Fe-NO stretching and bending modes of the heme-NO unit [3], an effect which can be related to a change of its electronic properties.

This work was supported by the research initiative NANOKAT and the German Federal Ministry of Education and Research under 05 K13UK2.

1. B. Moeser, A. Janoschka, J.A. Wolny, H. Paulsen, I. Fillipov, R.E. Berry, H. Zhang , A.I. Chumakov, F.A. Walker, V. Schünemann, J. Am. Chem. Soc. 134(9) (2012) 4216.

2.  B. Moeser, A. Janoschka, J. A. Wolny, I. Filipov, A.I. Chumakov, F. A. Walker, V. Schünemann, Hyperfine Interact. 206(1) (2012) 19.

3. H. Auerbach, I. Faus, S. Rackwitz, J. A. Wolny, F. A. Walker, A. I. Chumakov, H. Ogata, M. Knipp, V. Schünemann, Hyperfine Interact. 226 (2014) 439.