1971 - Insulin (PDB file 1INS)[23] is a hormone central to the metabolism of sugar and fat storage, and important in human diseases such as obesity and diabetes. It is biophysically notable for its Zn binding, its equilibrium between monomer, dimer, and hexamer states, its ability to form crystals in vivo, and its synthesis as a longer "pro" form which is then cleaved to fold up as the active 2-chain, SS-linked monomer. Insulin was a success of NASA's crystal-growth program on the space shuttle, producing bulk preparations of very uniform tiny crystals for controlled dosage.