After 1959, Perutz and his colleagues went on to determine the structure of oxy- and deoxy- haemoglobin at high resolution. As a result, in 1970, he was at last able to suggest how it works as a molecular machine: how it switches between its deoxygenated and its oxygenated states, in turn triggering the uptake of oxygen and then its release to the muscles and other organs. Further work over the next two decades refined and corroborated the proposed mechanism. In addition Perutz studied the structural changes in a number of haemoglobin diseases and how these might affect oxygen binding. He hoped that the molecule could be made to function as a drug receptor and that it would be possible to inhibit or reverse the genetic errors such as those that occur in sickle cell anaemia. A further interest was the variation of the haemoglobin molecule from species to species to suit differing habitats and patterns of behaviour. In his final years Perutz turned to the study of changes in protein structures implicated in Huntington and other neurodegenerative diseases. He demonstrated that the onset of Huntington disease is related to the number of glutamine repeats as they bind to form what he called a polar zipper.