Lyophilized protein was resuspended in either 100 or 250 mM
phosphate buffer in H2O or 100 mM phosphate in D2O. 10% v:v
D2O was added to the H2O samples. Protein concentration varied
from ~0.6 mM to ~3 mM (final volume of ~300 μL). Sample pH
ranged between 7.1 and 7.5. Iron reduction was performed by
adding 3- to 13-fold excess sodium dithionite (DT, Sigma-Aldrich).
Alternatively, freshly purified protein was concentrated, exchanged
in the appropriate buffer, and used without lyophilization.
Cyanomet CtrHb was generated by adding a 5-fold excess of potassium
cyanide (KCN) to ferric holoprotein solutions