1960 - The Hemoglobin crystal structure[4] showed a tetramer of two related chain types and was solved at much lower resolution than the monomeric myoglobin, but it clearly had the same basic 8-helix architecture (now called the "globin fold"). Further hemoglobin crystal structures at higher resolution [PDB 1MHB, 1DHB) soon showed the coupled change of both local and quaternary conformation between the oxy and deoxy states of hemoglobin,[5] which explains the cooperativity of oxygen binding in the blood and the allosteric effect of factors such as pH and DPG. For decades hemoglobin was the primary teaching example for the concept of allostery, as well as being an intensive focus of research and discussion on allostery.