The primary objective is to elucidate the stereochemical mechanism of hemoheme interactions (i.e. allosteric or cooperative subunit interactions) in human hemoglobin, by applying X-ray crystallographic and difference spectroscopy methods to the study of normal, abnormal, and chemically modified forms of the protein. Special emphasis is placed on structure determinations which resolve questions concerning the functional significance of intermediate quaternary states, which are thought to form, during the cooperative oxygenation process. Reactive analogues of 2 allosteric effectors for hemoglobin (i.e. analogues of 2,3-DPG and IHP) will be synthesized and made to react with its regulatory site, in order to produce covalently-complexed (2,3-DPG (or IHP): deoxyhemoglobin) crystals. Their structures and their UV or near IR difference spectras, before and after ligation with O2 or CO, should allow for the characterization of intermediate states. Natural and artifical hybrid forms (e.g. hemoglobins M and cyandeoxy hybrids) will be utilized in this work as models for the reaction of hemoglobin with ligands.