whether the D8 s phase could be stabilized at higher carbon contents. It seems clear, however, that the stability of the T1 binary phase with respect to the D8 s phase increases with increasing group number in the periodic table. Further studies of the germanides will undoubtedly strengthen this interesting and important analogy between these two groups of intermetallic compounds. NOWOTNY, H., PARTH~., E., KIEFFER, n. & BENESOVSKY, F. (1954). Mh. Chem. 85, 255.
NOWOTNY, H., SEARCY, A.W. ~5 eRR, J.E. (1956).J. Phys. Chem. 60, 677. PARTHI~, E. (1957). Powder Metallurgy Bulletin. 8, 23. Acta Cryst. (1958). 11, 17 The Crystal Structure of L-Leucyl-L-Prolyl-Glycine* :BY YUEN C. LEUNG AND I~ICtIkRD E. MARSH Technology, Passadena, California, U.S.A. (Received 15 January 1957) 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.
Gates and Crellin Laboratories of Chemistry, California Institute of
IntroductionAccurate determinations of the crystal structures of amino acids and simple peptides are of fundamental importance in arriving at the configurations of polypeptide chains in protein molecu]es. Such determinations yield information concerning the dimensions of * Contribution No. 2149 from the Gates and Crellin Laboratories of Chemistry. The work described in this article was carried out under a contract ) between the Office of Naval Research and the California Institute of Technology. the various components of the polypeptide chain, the methods of packing of the side chains, and the role of hydrogen bonding in determining the spatial arrangements of the chains. The confidence which can be placed in predictions of these various structural features of a protein--and, hence, the confidence with which the structure of a protein as a whole can be predicted--depends directly on both the number and the accuracy of the experimental results derived from the simpler compounds.The amino acid proline is an important constituent ACll 2
TI=IE CI~YSTAL STRUCTURE OF L-LEUCYL-T,-PI~OLYL-GLYCINEof many proteins; for example, approximately 12% of the amino-acid residues in gelatin and collagen are proline and another 10 % of the residues are hydroxyproline. Structurally, proline and hydroxyproline are especially important. The nitrogen atoms in these residues have no attached hydrogen atoms an...
