of biological systems. This financial support allowed him to establish the Molecular Biology Unit at the Cavendish Laboratory. Perutz's new unit attracted researchers who realised that the field of molecular biology had great promise, among them were Francis Crick in 1949 and James D. Watson in 1951. In 1953 Perutz showed that diffracted X-rays from protein crystals could be phased by comparing the patterns from crystals of the protein with and without heavy atoms attached. In 1959 he employed this method to determine the molecular structure of the protein haemoglobin, which transports oxygen in the blood. This work resulted in his sharing with John Kendrew the 1962 Nobel Prize for Chemistry. Nowadays the molecular structures of several thousand proteins are determined by X-ray crystallography every year. 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. DNA structure and Rosalind Franklin During the early 1950s, while Watson and Crick were frantically trying to determine the structure of deoxyribonucleic acid (DNA), they were given by Perutz an unpublished 1952 progress report for the King's College laboratory of Sir John Randall. This report contained X-ray diffraction images taken by Rosalind Franklin, that proved to be crucial in coming to the double-helix structure. Perutz did this without Franklin's