Quaternary structure, hydration, and self-association of hemoglobin. A proton magnetic relaxation study.

The hydration of oxyhemoglobin, carbonylhemoglobin, and deoxyhemoglobin does not depend on the quaternary state of the hemoglobin molecule as revealed through the concentration dependence of proton magnetic relaxation rates. The biphasic relaxation behavior of isotopically diluted solutions of hemoglobin confirms that the self-association of hemoglobin molecules at higher concentration is independent of the quaternary structure. In the case of aquomethemoglobin, a biphasic relaxation and a diminished heme accessibility at higher concentrations are observed, caused by interaction of the associating hemoglobin molecules.