First X-ray diffraction pattern of a protein crystal (pepsin)

In 1934, working alongside her mentor J.D. Bernal at Cambridge, Dorothy Crowfoot obtained the first successful X-ray diffraction photograph of a protein crystal — pepsin, a digestive enzyme. This was a landmark achievement: previous attempts to X-ray protein crystals had failed because the crystals lost their ordered structure when they dried out and were exposed to air.

Bernal and Crowfoot discovered that protein crystals needed to remain in their mother liquor — that is, hydrated — in order to preserve the regular diffraction pattern that revealed their internal molecular order. This insight was revolutionary: it opened the door to the entire field of protein crystallography, a technique that would eventually allow scientists to determine the atomic structures of proteins, enzymes, viruses, and other complex biomolecules.

The 1934 pepsin diffraction pattern is widely regarded as a founding moment of structural molecular biology. It demonstrated for the first time that proteins possessed a definite, orderly three-dimensional structure that could, in principle, be solved atom by atom using X-rays — a project that would occupy Hodgkin and generations of scientists after her. This early breakthrough, achieved when Hodgkin was only in her early twenties and one of very few women working in the field, established her scientific reputation and set the trajectory for her life's work.