Angular dependence of dipole-dipole-Curie-spin cross-correlation effects in high-spin and low-spin paramagnetic myoglobin

The ¹⁵N-HSQC spectra of low-spin cyano-met-myoglobin and high-spin fluoro-met-myoglobin were assigned and dipole-dipole-Curie-spin cross-correlated relaxation rates measured. These cross-correlation rates originating from the dipolar ¹H-¹⁵N interaction and the dipolar interaction between the ¹H and the Curie spin of the paramagnetic center contain long-range angular information about the orientation of the ¹H-¹⁵N bond with respect to the iron-¹H vector, with information measurable up to 11 Å from the metal for the low-spin complex, and between 10 to 25 Å for the high-spin complex. Comparison of the experimental data with predictions from crystal structure data showed that the anisotropy of the magnetic susceptibility tensor in low spin cyano-met-myoglobin significantly influences the cross-correlated dipole-dipole-Curie-spin relaxation rates.