Is it 6? I would assume it is six, but have no idea.
All of my biology classes are failing me. I thought that it was 2, at least in the case of hemoglobin.
Lehninger’s Principles of Biochemistry states that the iron is in the +2 (Ferrous) state as stated by chaoticdonkey. Also, according to Lehninger, hemoglobin has a quaternary structure of four alpha-beta (sorry don’t know how to add Greek letter symbols to postings) protein subunits.
Well DUH! I could have told you that. 