The crystal structure of L -leucyl- L -prolylglycine

The crystal structure of the tripeptide leucyl-prolyl-glycine 'mono'-hydrate has been determined by Fourier and least-squares analysis of complete three-dimensional intensity data from copper radiation. The crystals are monoclinic with space group P21 ; the unit-cell dimensions are : a 0 = 9-44, b 0 = 6.72, c o ----12.10 /~, fl ----100.2 . With the exception of a twist required by the presence of the proline ring, the peptide chain is in a highly extended configuration. A surprising feature is the presence of only approximately 80 % of a water molecule of crystallization per molecule of tripeptide. In addition, one atom in the pyrrolidine ring of the proline residue is disordered, being located with apparently equal probability on either side of the plane of the other four ring atoms.