To determine three-dimensional molecular structures, scientists first needed to crystalize the molecule. These beautiful crystals from a MOPC603 tumor immunoglobulin were created by Potter’s postdoc Stuart Rudikoff in the 1970s. Potter took the crystals to his colleague David Davies (National Institute of Diabetes and Digestive and Kidney Diseases), who used x-ray diffraction to determine their three-dimensional structure. This was the very first time that the structure of an amino acid chain—the binding site of an immunoglobulin, with a known antigen-binding specificity—had ever been described.

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