T. Ashida

An X-ray study of the synthetic polypeptide (Pro-Pro-Gly)10

Abstract A polypeptide, (Pro-Pro-Gly) 10 , synthesized as a collagen model, gave a single crystal suitable for X-ray analysis with unit cell dimensions a = 26.9, b = 26.4, c = 100.4 A , and space group P 2 1 2 1 2 1 . The unit cell consists of four triple helices, whose locations are indicated on a tentative electron-density projection along the fiber axis. The helical parameters obtained from the three-dimensional intensity distribution and Patterson maps are: major helix radius 2.8 A; major helix pitch 60.24 A; vertical distance (parallel to c axis) between residues 2.87 A; number of residues in the repeat distance 21; and number of turns of minor helix in the repeat distance 7.

tert-Butyloxycarbonyl-l-cysteinyl-l-cysteine disulfide methyl ester

C t2H20N2OsS2, orthorhombic, P2t2~2 ~, a = 17.404 (1), b = 10.565 (2), c = 9. 137 (5) /~, O m = 1.328 (by flotation in CCl4-n-hexane), D x = 1.330 g cm 3 for Z = 4. The title compound is a cyclo cystine compound. The structure was solved by direct methods and refined by the block-diagonal least-squares technique to a final R of 0.078 (R w = 0-065). The peptide group has a cis conformation. The torsion angle about the S S bond is 95.7 ° and those about the two S C bonds are 7 6 . 8 and 4 8 . 6 ° . Introduction. Colorless, transparent, needle-shaped single crystals elongated along e were obtained by slow evaporation from a mixture of ethyl acetate and chloroform. A crystal with dimensions 0.2 × 0.3 x 0.5 mm was used for the X-ray analysis. The unit-cell dimensions were obtained by least-squares refinement of the settings of 13 reflections measured on a diffractometer. Intensity data were measured on an automatic Rigaku four-circle diffractometer, equipped with a rotating anode, using graphite-monochromated Mo K~ radiation (2 = 0.71069 A) and a monitorcounting technique. The 0-20 scan mode with a scan rate of 16 ° min -~ in 20 was employed. The 0 scan range was calculated as (1.2 + 0.35 tan 0) °. Intensity data of 2314 independent reflections were collected with (sin 0)/2 <_. 0.66 Al ; of these, 200 were measured with I/7,,I = 0.0. No absorption correction was applied [fl(Mo K¢0 = 3.32 cm-t] . The structure was solved by direct methods, using the symbolic addition method for noncentrosymmetric crystals (Karle & Karle, 1966) and the weighted tangent-formula technique (Germain, Main & Woolfson, 1971). All nonhydrogen atoms were * Present address: Department of Applied Chemistry, Faculty of Engineering. Nagoya University, Chikusa-ku, Nagoya 464, Japan. located from the E map based on the phases of 281 reflections with IEI >_ 1.2. The parameters were refined by block-diagonal least-squares calculations with HBLS-5 (Ashida, 1973), first using isotropic temperature factors and then anisotropic. The quantity minimized was Z w(IFol -IFcl) 2. A difference map revealed the positions of all but two of the H atoms. The contributions of the H atoms to the structure factors were included in further refinement, but their parameters were not refined; their thermal parameters were assumed to be isotropic (B = 3.8 A2). The final R is 0.078 for 2114 non-zero reflections and R w = IZw(IFol IFcl)2/EwlF,,12l~/2 was 0.065 for all reflections. The weighting scheme finally adopted was w = 0.2 for IF, I --0.0 and w = [a2(F,,) + O.O011F,,12l in for IFol > 0.0. The atomic coordinates are given in

The crystal structure of tert-butyloxycarbonyl-l-prolyl-l-leucylglycine hydrate

Enraf-Nonius Structure Determination Package (1975). Manual edited by B. FRENZ & Y. OKAVA. Molecular Structure Corporation, College Station, Texas, USA. JOHNSON, C. K. (1976). ORTEP II. Report ORNL-5138. Oak Ridge National Laboratory, Tennessee. PRZYBYLSKA, M. (1974). Acta Cryst. B30, 2455-2459. SPEAKMAN, J. C. (1967). Chem. Commun. pp. 32-33. SRIVASTAVA, S. N. • PRZYBYLSKA, M. (1969). Acta Cryst. B25, 1651-1658. StrrroN, L. E. (1965). Tables of Interatomic Distances and Configuration in Molecules and Ions. London: The Chemical Society.

cis-Proline in the Linear Oligopeptide: Structure of Benzyloxycarbonyl-glycyl-prolyl-leucine

The crystal structure of a racemic compound of benzyloxycarbonyl-Gly-L-Pro-L-Leu and its enantiomorph has been determined. The crystallographic data are: P21/a, a = 22.126 (9), b = 9.615 (7), c= 10185 (5) A, fl = 9623 (4) °, Z= 4. The final R value is 0059. The peptide bond between the glycyl and prolyl residues has a cis conformation, and the bond angles around the N(Pro) atom are significantly affected by the internal rotation of the peptide bond. The angle/_C-N-C ~ is larger and the angle/_C-N-C ° is smaller, respectively, than those in the trans form. The torsion angles of the prolyl residue agree essentially with those of poly-L-proline I.