At the record low age of 25, Lawrence Bragg received the Nobel Prize in Physics 1915 jointly with his father. The young man had developed a theory for X-ray diffraction, which he and his father used to determine the structure of simple molecules, like NaCl. In 1968, more than 50 years later, when Bragg for the first and only time visited the Lindau meetings, he had a fascinating story to tell. In 1938 he succeeded Ernest Rutherford as director of the Cavendish physics laboratory in Cambridge. There a small group around J.D. Bernal had started to take an interest in the structure of protein molecules. A young Austrian, Max Perutz, had already started to study haemoglobin. Under Bragg’s enlightened directorship, the group expanded with John Kendrew (myoglobin) and Francis Crick and James Watson (DNA). During the 1950’s the structures of the complicated molecules were finally revealed. For this work, in 1962, Perutz and Kendrew received Nobel Prizes in Chemistry, while at the same time Crick and Watson received Nobel Prizes in Physiology or Medicine! In his lecture at Lindau, Bragg describes the complexity of the crystallographic procedure. This starts with attempts to make usable crystals out of the biologically interesting large molecules. The crystals are irradiated with X-rays from all possible angles and the diffraction patterns are recorded on many thousands of photo plates. At the end, a mathematical treatment is needed to interpret the locations and intensities of the spots of the diffraction patterns. A haemoglobin molecule has about 10 000 atoms, which means that there are about 100 000 000 pairs of atoms, the relative positions of which have to be determined. Even with the help of the newly invented electronic computing machines, this turned out to be a formidable task. A measure of this task is, e.g., that it took Max Perutz 25 years to unravel the structure of haemoglobin!

Anders Bárány