I have a HEME covalently attached to an amino acid side chain. From mass spec, the original sample was around 50/50 covalent attachment or unlinked. I have created a new library file to deal with the covalently linked HEME. Is there a way to refine the occupancy? I need to constrain the new residue B167 to the original amino acid A167 AND the original HEME A350. If I just do the normal occupancy refinement the new B167 gets constrained only to the original side chain A167. Or (since there isn't any large change in atom position) will the occupancy refinement be meaningless anyway? It's not like different orientations - just different bonding.