The structure of horse methaemoglobin at 2-0 A resolution

The structure of horse methaemoglobin has been redetermined by phase extension and refinement. This has improved our knowledge of the haem geometry and the stereochemistry of the interfaces between the subunits, and confirmed the disorder of the C-terminal residues. Using new four-circle diffractometer data between the limiting spheres of radius 10 and 2.0 Å^?1, the co-ordinates determined by Perutz et al. (1968a,b) were subjected to successive cycles of real-space refinement into electron density maps calculated with observed ¦F¦ values and phases derived from the latest refined model, until the reliability index had dropped from an initial value of 0.45 to 0.23. The positions of the iron atoms relative to the planes of the porphyrin rings were refined separately, and checked by Fourier syntheses based on anomalous scattering and by difference Fourier syntheses calculated with coefficients from which the iron contributions had been removed. The general root-mean-squared error in atomic positions is 0.32 Å; the probable error in the displacement of the iron atoms from the porphyrin planes is 0.06 Å. The difference Fourier synthesis, obtained after refinement of the protein was complete, showed 41 bound water molecules per asymmetric unit and also revealed five errors in amino acid sequence, one of which was confirmed chemically.The secondary structures of the subunits are stabilized by hydrogen bonds formed by main-chain NH and CO groups either with each other or with nearby polar side-chains. There are few internal hydrogen bonds linking the various chain segments; many of the external polar side-chains help to stabilize the tertiary structure by forming hydrogen bonds with each other or through bound water molecules. Several of the helical segments are irregular and the terminal residues are disordered. The contacts between the subunits are more polar than the earlier 2.8 Å map had led us to believe, because it had failed to show up the 15 bound water molecules at the α₁β₁ and the four at the α₁β₂ contact. Their inclusion has raised the number of hydrogen bonds between neighbouring subunits at α₁β₁ from five to 17 or possibly 19, and at α₁β₂ from two to six or possibly seven. The remaining 22 water molecules are distributed over the internal cavity and the molecular surface; most of them make hydrogen bonds with at least two polar groups of the protein. Despite several amino acid differences, the structure of the α₁β₁ contact, including the bound water, is the same as in human deoxyhaemoglobin (Fermi, 1975).     

Crystal and molecular structures of cyclomaltoheptaose inclusion complexes with HI and with methanol

β-Cyclodextrin (β-CD; cyclomaltoheptaose; cyclohepta-amylose; C₄₂H₇₀O₃₅) crystallises from aqueous solutions of HI and of MeOH in the form of stout prisms, which are isomorphous to each other with monoclinic space-group P2₁; cell constants for C₄₂H₇₀O₃₅ · 2HI · 8 H₂O: a = 21.25(3), b = 10.28(2), c = 15.30(2) Å, β = 113.25(9)°, and Z = 2; and for C₄₂H₇₀O₃₅ · MeOH · 6.5 H₂O: a = 21.03(3), b = 10.11(2), c = 15.33(2) Å, β = 111.02(9)°, and Z = 2. X-ray counter data were used to determine the structures of both crystals, which belong to the cage type, with β-CD molecules in nearly identical, “round” shapes. In the HI complex, one I^- is located inside, and one outside, the β-CD cavity; in the MeOH complex, the MeOH is within the cavity. The cavity is closed at the O-2,O-3 side by adjacent β-CD molecules, and at the O-6 side by water molecules hydrogen-bonded to the guest and to surrounding β-CD molecules. Interstices between β-CD molecules are filled by water of hydration molecules in distorted co-ordination.     

Structural components of alginic acid. II. The crystalline structure of poly-alpha-L-guluronic acid. Results of x-ray diffraction and polarized infrared studies

A structural investigation of the marine algal polysaccharide poly-α-L -guluronic acid is described. The molecular chains consist of 1 → 4 diaxially linked L -guluronic acid residues in the 1C chair conformation and are stabilized in a twofold helix conformation by an intra-molecular O(2)H … O(6)D hydrogen-bond. The X-ray fiber diffraction photograph has been indexed to an orthorhombic unit cell in which a = 8.6 Å, b (fiber axis) = 8.7 Å, c = 10.7 Å. A structure corresponding to the space group P2₁2₁2₁ is proposed, in which all intermolecular hydrogen bonds interact with water molecules and in which all oxygen atoms except for the inaccessible bridge oxygens are involed. The relationship between the shape and structure of the polyguluronic acid molecule and its biological function is discussed.     

Synthesis,structural characterization,and properties of the organothorium alkylthiolate complex [(CH3)5C5]2Th(SCH2CH2CH3)2

This contribution reports the synthesis and characterization of the organothorium alkylthiolate complex [(CH₃)₅C₅]₂Th(SCH₂CH₂CH₃)₂. This compound crystallizes in the monoclinic space group C2/c (#15) with four molecules in a cell of dimensions a=19.066(2), b=11.603(1), c=16.379(2) Å, and β=130.08(1)°. Least-squares refinement led to a value for the conventional R index (on F_o) of 0.040 for 132 variables and 2030 observations having F_o²⩾3σ(F_o²). The molecular structure consists of an unexceptional ‘bent sandwich’ [(CH₃)₅C₅]₂Th fragment coordinated to two n-propylthiolate ligands. The ThS bond distance is 2.718(3) Å; the SC(α) distance, 1.78(2) Å; the ThSC(α) angle, 108.3(5)°; and the SThS′ angle, 102.5(2)°. Contrasts are drawn with the structures of analogous actinide alkoxides     

The crystal and molecular structure of O-α-D-mannopyranosyl-(1→3)-O-β-D-mannopyranosyl-(1→4)-2-acetamido-2-deoxy-α-D-glucopyranose

The crystal structure of α-D-Manp-(1→3)-β-D-Manp-(1→4)-α-D-GlcNAcp has been determined by the direct method using the multi-solution, tangent formula, and “magic integer” procedures. The space group is P2₂, and 2 molecules are in the unit cell with a  9.894 (5), b  10.372 (6), c  11.816 (6) Å, and β  95.03° (6). The structure was refined to R 0.059 for 2099 reflections measured with Mo Kα radiation. Difference synthesis showed all the hydrogen atoms, and indicated a partial (～30%) substitution of the α-anomer molecules by the β-anomer molecules. The D-mannopyranose and the D-glucopyranose have the normal ⁴C₁ conformation; an intramolecular hydrogen-bond O-3″-H.....O-5′ (2.703 Å) stabilises the GlcNAc in relation to β-D-mannopyranose.     

A preliminary crystallographic study of isocitrate dehydrogenase from Azotobacter vinelandii

Large single crystals of isocitrate dehydrogenase from Azotobacter vinelandii have been grown by vapor diffusion from ammonium sulfate and phosphate solutions. The crystals are tetragonal, space group P4₂2₁2 with cell dimensions $\text{a = 122.1}\text{A}\text{?}$, $\text{c = 163.9}\text{a}\text{?}$. There are two molecules of 80,000 molecular weight per asymmetric unit. Native data to 5.5 Å resolution have been collected on a diffractometer. A rotation function using data between 10 Å and 6 Å resolution indicates three possible orientations of the non-crystallographic 2-fold axis relating the two molecules.     

Methyl 2-methoxy-7-(4-methylbenzoyl)-4-oxo-6-p-tolyl-4H-furo[3,2-c]pyran-3-carboxylate:A combined experimental and theoretical investigation

The title compound, methyl 2-methoxy-7-(4-methylbenzoyl)-4-oxo-6-p-tolyl-4H-furo[3,2-c]pyran-3-carboxylate (C₂₅H₂₀O₇), was prepared and characterized by IR and single-crystal X-ray diffraction (XRD). The compound crystallizes in the triclinic space group P ?1 with a?=?8.9554(9) Å, b?=?10.0018(10) Å, c?=?12.7454(13) Å, α?=?67.678(7)°, β?=?89.359(8)° and γ?=?88.961(8)°. In addition to the molecular geometry from X-ray experiment, the molecular geometry and vibrational frequencies of the title compound in the ground state have been calculated using semiempirical AM1 and PM3 methods, as well as Hartree-Fock (HF) and density functional (B3LYP) levels of theory with 6–31G(d) basis set. To determine conformational flexibility, molecular energy profile of the title compound was obtained by semi-empirical (AM1) calculations with respect to two selected degrees of torsional freedom, which were varied from ?180° to +180° in steps of 10°. Besides, frontier molecular orbitals (FMO) analysis and thermodynamic properties of the title compound were performed by the B3LYP/6–31G(d) method.     

Characterization of crystals of a cytochrome oxidase (nitrite reductase) from Pseudomonas aeruginosa by x-ray diffraction and electron microscopy

Cytochrome oxidase from Pseudomonas aeruginosa has been crystallized from 2 m-ammonium sulfate. The crystals occur principally as thin diamond-shaped plates of space group P2₁2₁2 with unit cell dimensions of 92 Å × 115 Å × 76 Å. Determination of the density of glutaraldehyde-fixed, water-equilibrated crystals (1.167 g/cm³), coupled with the unit cell volume (804,000 ų), indicates that there is one subunit (~63,000 Mr) per asymmetric unit. X-ray diffraction data which were limited to 12 Å resolution due to small crystal size were obtained for the hk0 and 0kl zones using precession photography. Amplitude and phase data for the hk0, 0kl, and h0l zones were obtained from computer-based Fourier analysis of appropriate micrographs recorded from negatively stained microplates and thin sections of larger crystals using minimal beam electron microscopy. For crystals embedded in the presence of tannic acid it was possible to achieve 20 Å resolution which is comparable to the resolution achieved with negative staining of thin crystalline arrays. In addition, unstained electron diffraction on glutaraldehyde-fixed, glucose-stabilized plates was recorded to a resolution of 9 Å. The three-dimensional packing of the cytochrome oxidase dimer in the unit cell has been deduced from computer reconstructed images of the three principal projections along the crystallographic axes. The cytochrome oxidase dimer is located in the unit cell with the dimer axis coincident with a crystallographic 2-fold axis; thus within the resolution of the present data in projection (9 Å) the two subunits are identical, in agreement with biochemical evidence. The crystals have been prepared with the enzyme in the fully oxidized state and upon reduction a progressive cracking of the crystals is observed, possibly due to a conformational change dependent on the oxidation state of the heme iron.     

Structure and stereochemistry of stenophyllolide,a germacrolide from Centaurea aspera var. Stenophylla

A crystalline compound, named stenophyllolide, obtained from an extract of Centaurea aspera var. stenophylla was shown to be 9β,15-dihydroxygermacra-1(10),4,11-trien-6α,12-olide by X-ray analysis. The molecular structure of stenophyllolide was solved with orthorhombic space group P2₁2₁2₁, a = 11.719 (5), b = 13.389 (5), c = 8.646 (5) Å for Z = 4, by direct methods and refined to a final R of 0.06 for 1198 observed reflections.     

Solution Structure of a Parallel Left-handed Double-helical Gramicidin-A Determined by 2D1H NMR

The structure of a parallel left-handed double-helical form of gramicidin was detected by circular dichroism spectroscopy and determined using 500 and 600 MHz NMR in CaCl₂/methanol solution. Measurements of TOCSY, DQF-COSY and NOESY spectra were converted into 604 distance and 48 torsional angle constraints for structure calculations. Stereospecific assignments and χ₁angles were calculated using³J_αβ, d_αβ(i,i), d_Nβ(i,i) and d_Nγ(i,i). χ₂angles were determined using d_αβ(i,i), d_Nβ(i,i), d_βδ(i,i), d_Nγ(i,i) and d_αγ(i,i). The calculations of initial structures were performed using the distance geometry/simulated annealing method in XPLOR. The initial structures were further refined and energy minimized using simulated annealing/molecular dynamics methods. Back-calculations for every generated structure were also performed to check their consistency with the experimental data.187 final structures with no violations above the threshold conditions (0.05 Å, 5°, 5°, 0.5 Å and 5° for bonds, angles, improper, NOE and cdihe, respectively) were produced from the 200 initial structures. Twenty structures with the lowest NOE energies were used for further analysis. The average r.m.s. deviations for the 20 structures are 0.64 Å for backbone and 1.1 Å for all non-hydrogen atoms.Gramicidin in this form, with approximately 5.7 residues per turn, is a parallel double helical dimer. The length along the helix axis is about 30 Å and the inner pore diameter varies from 1 to 2 Å. It is different from all other gramicidin structures determined to date. The presence of Ca^{2 +}stabilises a conformation that prevents the binding of monovalent cations. It is likely that this structure is related to a non-channel, antibiotic role of gramicidin.     

Solution and solid state behavior of Co2+, Ni2+ and Zn2+ tosylaminoacidate systems: Crystal and molecular structure of bis(N-tosylglycinato)tetraaquocobalt(II) and bis(N-tosyl-β-alaninato)tetraaquozinc(II) complexes

The interactions between N-tosylamino acids and cobalt(II), nickel(II) and zinc(II) ions in aqueous solution and in the solid state have been investigated. From concentrated aqueous solutions, compounds of general formula [M(II)(N-tosylaminoacidato)₂(H₂O)₄](M = Co(II), Ni(II) and N-tosylaminoacidato = N-tosylglycinate (Tsgly^?), N-tosyl-α- and -β-alaninate (Ts-α- and Ts-β-ala^?); M = Zn(II) and N-tosylaminoacidate = Tsgly^?, Ts-β-ala^?) and [Zn(II)(N- tosylaminoacidato)₂(H₂O)₂] were isolated and characterized by means of thermogravimetric, electronic and infrared spectra. For two of them: [Co(Tsgly)₂(H₂O)₄](I) and [Zn(Ts-β-ala)₂(H₂O)₄](II) the crystal and molecular structures were also determined. Both compounds crystallize in the monoclinic space group P2₁/c, with two formula units in a cell of dimensions: a = 13.007(6), b = 5.036(2), c = 18.925(7) Å, β = 102.33(3)° for (I) and a = 14.173(6), b = 5.469(2), c = 17.701(7) Å, β = 106.63(3)° for (II). The structures were solved by the heavy-atom method and refined by least-squares calculations to R = 0.031 and 0.064 for (I) and (II) respectively. The cobalt and zinc atoms lie in the centers of symmetry, each bonded to two amino- acid molecules through a carboxylic oxygen atom and four water molecules in a slightly tetragonally distorted octahedral geometry. The second carboxylic oxygen atom is not involved in metal coordination. Electronic and X ray-powder spectra suggest that the tetrahydrate complexes of Co²⁺, Ni²⁺ and Zn²⁺ ions of the same amino acids are isomorphous and isostructural. No coordinative interactions between ligand and metal ions were found in aqueous solution on varying the pH values before hydroxide precipitation.     

The crystal and molecular structure of a 3:2 mixture of laminarabiose and O-α-d-glucopyranosyl-(1→3)-β-d-glucopyranose

The crystal and molecular structure of a 3:2 mixture of laminarabiose and 3-O-α-d-glucopyranosyl-β-d-glucopyranose has been determined by X-ray diffraction. The crystal belongs to the monoclinic system, space group P2, a 14.778(1), b 4.794(1), c 10.516(1) Å and β 98.10(1)^c, Dm 1.54 g. cm^-3, Z 2. The structure was solved by the direct method and refined by the block-diagonal, least-squares procedure to R 0.057 for 1034 observed reflections. Difference synthesis showed all hydrogen atoms and indicated a partial (～39%), random substitution of the β anomer molecules by the α anomer molecules, which are accompanied by water molecules on the crystallographic two-fold axis (～19%). The molecule shows a conformation, different from the fully-extended one, which is stabilized by an intramolecular hydrogen-bond between O-1-H and O-5 [2.786(7) Å]. The ring-to-ring conformation can be described as (Φ, Ψ)=(27.9·–37.5·), according to the definition of Sathyanarayana and Rao, and it is located in the comparatively low-energy region of the energy-contour diagram of laminarabiose. Four intermolecular hydrogen-bonds hold molecules together to form infinite sheets, which are approximately parallel to the ab-plane and linked by additional hydrogen-bonds in the c-direction.     

Crystal and molecular structures of substituted α-d-glucopyranosides

The crystal and molecular structures of methyl 2,4,6-tri-O-pivaloyl-α-d-glucopyranoside (1), methyl 4,6-O-(R)-benzylidene-2-O-pivaloyl-α-d-glucopyranoside (2), and methyl 4,6-O-(R)-benzylidene-2,3-di-O-pivaloyl-α-d-glucopyranoside (3) were determined by X-ray analysis. Crystals of 1 are orthorhombic, space group P2₁2₁2₁ with the unit cell a = 13.026(2), b = 16.832, c = 11.929(2) Å, Z = 4. Crystals of 2 are monoclinic, space group P2₁. The unit-cell parameters are a = 6.519(1), b = 14.664(4), c = 10.635(4) Å, β = 93.18(1)°, Z = 2. Crystals of 3 are orthorhombic, space group P2₁2₁2₁ with a = 10.006(3), b = 13.874(3), c = 18.527(5) Å, Z = 4. The structures were solved by MULTAN and refined by a full-matrix procedure to final values of R = 0.084 (1), 0.048 (2), and 0.069 (3). The pyranose ring in each compound adopts the ⁴C₁ conformation. The 1,3-dioxane rings in 2 and 3 show a chair conformation. The molecular packing in 1 is through the hydrogen bonds involving HO-3 and the 6-O-pivaloyl carbonyl group [HO-3 ⋯ O-9, 2.855(8) Å], which connect the molecules into a chain along

. The endocyclic oxygen atom is involved in an intermolecular hydrogen-bond with HO-3 [2.848(4) Å], joining molecules of 2 into the chains along

. There are no free hydroxyl groups in 3 and molecular packing reflects van der Waals interactions only.     

Stochastic processes in particle-number fluctuations in an electron-photon shower

The paper is concerned with the existence and asymptotic character of the nonlinear boundary value problemdG/dt=F(t,G,F, ¦α?β¦) (1) ¦α?β¦dF/dt=g(t,G,F, ¦α?β¦)G(o,¦α?β¦)=k ₁,G(∞,¦α?β¦)=k ₂ (2) as ¦α?β¦→ o+ The discussion is related to the problem of particle-number fluctuations in the theory of cosmic radiation andG andF denote respectively the probability generating functions for the electron distribution in an electron-initiated and a photon-initiated shower. A solution of the system (1) satisfying the boundary conditions (2) is constructed so that specified limiting conditions are fulfilled.     

Preparation and crystal structure of bis(acetato)(trans-1,2-diaminocyclohexane)platinum(II)

The structure of the complex [Pt(trans-1,2-di- aminocyclohexane) (acetate)₂]·H₂O has been determined by X-ray diffraction. This racemic compound is orthorhombic, space group Aba2, a = 20.813(9), b = 7.926(5), c = 17.296(8) Å, Z = 8. The structure was refined on 1214 nonzero Cu Kα reflections to R = 0.028. The square planar environment of Pt includes the amino groups of the diamine in cis positions and oxygens from two monodentate acetates. The PtN and PtO distances average 2.00(3) and 2.02(3) Å, respectively. The bite of the diamine ligand imposes a NPtN angle of 85(1)°, whereas the small OPtO angle of 85(1)° probably results from packing effects. The average plane through the puckered cyclohexyl ring makes an angle of 19° with the PtN₂O₂ plane. The molecules are stacked by pairs along the b axis. The two molecules of each pair are 180° apart about the stacking axis, and form altogether four NH···O hydrogen bonds.     

Identification of a structural hairpin in the filamentous chimeric phage M13Gori1

Crystals of alkaline phosphatase (EC 3.1.3.1; M_r 94,000) grown at pH 9.5 from 2.25 m-(NH₄)₂SO₄ with 5 × 10^?5 m-Zn and 10^?2 m-Mg present were analyzed by X-ray diffraction at pH 7.5 in 2.66 m-(NH₄)₂SO₄ with 10^?2 m-Zn and 10^?2 m-Mg present. The crystals are orthorhombic with $\text{a = 195.5}\text{A}\text{?}\text{, b = 168.3}\text{A}\text{?}\text{and}\text{c = 76.33}\text{A}\text{?}$, and the space group is I222. X-ray phases were determined by the multiple isomorphous replacement and anomalous dispersion method using K₂PtCl₄, KAu(CN)₂ and K₂OsO₄ derivatives. The electron density maps and analysis of metal binding sites reveal one molecule per asymmetric unit with an internal, non-crystallographic, 2-fold rotation axis relating the subunits. Each subunit contains a major $\text{α}\text{β}$ domain with a seven-stranded β-sheet flanked by helices. The sheets are roughly coplanar but the general direction of the strands in each is at 20 ° to the rotation axis and thus 40 ° from each other. The helical content of the $\text{α}\text{β}$ domain is approximately 27% of the 459 residues in the monomer and the β content is approximately 7%. The chains in a smaller domain are more convoluted and less easily characterized than in the $\text{α}\text{β}$ domain. In both there is extensive monomer-monomer contact.Removal of the zinc and magnesium from the parent crystal produces a stable apoenzyme crystal and addition of cobalt at 10^?2 m or cadmium at 10^?2 or 5 × 10^?2 m reveals seven metal binding sites per dimer. The active centers are 32 Å apart and each is shown by anomalous dispersion data to contain two metal binding sites, A and B. The cadmium derivative refinement determined the A-B separation to be 4.9 Å. Comparison of the parent and apo structures by means of difference maps reveals the double metal site with Zn at A and probably Mg at B. A prominent, partially resolved peak centered 7 Å away is interpreted as a stabilization of the backbone in this position by the metal ion co-ordination to a side-chain. Several negative peaks within 10 Å of the metals indicate local differences between apo and native structures but no significant differences are seen in the other parts of the molecule. At 5 × 10^?2 m-Cd two metal sites (D and D′) are found 25.5 Å from the active center, on the surface of the minor domain. They are related to each other by the molecular 2-fold axis with a D-D′ distance of 25 Å. The seventh Cd site, E, is 20 Å from the active center, on the major domain, near a crystalline contact region, and devoid of any molecular symmetry mate.The apparent dissociation constants for cadmium at the A, B and D sites (and A′, B′, D′) are 3 × 10^?3 m, 1.5 × 10^?1 m and 1.3 × 10^?2 m, respectively. Thus in these conditions cadmium is seen to distribute between A and B sites when the combined stoichiometry is two metal ions per dimer.     

Studies on the metal—amide bond. XVII. The crystal and molecular structure of the α-form of aqua[N,N′-bis(2′-pyridinecarboxamido)-1,3-propane] copper(II) dihydrate

α-Aqua[N,N′-bis(2′-pyridinecarboxamido)-1,3-propane]copper(II) dihydrate, C₁₅H₂₀N₄O₅Cu, is monoclinic, space group P2₁/c, with a = 11.719(2), b = 13.092(2), c = 12.663(2) Å, β = 119.56(1)°, Z = 4. The structure was refined to R = 0.026 for 2398 diffractometer data using full-matrix least-squares methods. The copper atom is five-coordinate with the N₄-tetradentate ligand encompassing the base of a distorted square-based pyramid which is appreciably distorted towards a trigonal bipyramid [average Cu-N(amide) 1.950(2), Cu-N(pyridine) 2.043(2) Å, N(amide)-Cu-N(amide) 94.5(1), N(pyridine)-Cu-N(pyridine) 100.2(1)°] and with the copper atom lying 0.27 Å above the N₄ plane towards the apical water molecule [Cu-O 2.236(2) Å]. The central six-membered chelate ring adopts a skewed boat conformation and the enforced strain in the molecule results in non-planar distortions in the pyridine rings with only small distortions in the amide groups. The molecules pack in sheets parallel to (10$\text{1}$) and the hydrogen-bonding network involves the water molecules and the amide oxygen atoms of the ligand.     

Crystallization,preliminary X-ray diffraction study,and crystal packing of a complex between anti-Hen lysozyme antibody F9.13.7 and Guinea-fowl lysozyme

The complex formed between the Fab fragment of a murine monoclonal anti-hen egg lysozyme antibody F9.13.7 and the het-erologous antigen Guinea-fowl egg lysozyme has been crystallized by the hanging drop technique. The crystals, which diffract X-rays to 3 Å resolution, belong to the monoclinic space group P2₁, with a = 83.7 Å, b = 195.5 Å, c = 50.2 Å, β = 108.5° and have two molecules of the complex in the asymmetric unit The three-dimensional structure has been determined from a preliminary data set to 4 Å using molecular replacement techniques. The lysozyme–Fab complexes are arranged with their long molecular axes approximately parallel to the crystallo-graphic unique axis. Fab F9.13.7 binds an anti-genie determinant that partially overlaps the epitope recognized by antilysozyme antibody HyHEL10. © 1993 Wiley-Liss, Inc.     

Crystal and molecular structure of Δ-cis-α-ethylenebis-S-prolinato(1,2-diamino-ethane)cobalt(III) perchlorate dihydrate, Δ-cis-α-[Co(ss-EBP)(en)] ClO4·2H2O

The crystal and molecular structure of Δ- cis-α- ethylenebis-S-prolinato(1,2-diaminoethane)cobalt(III) perchlorate dihydrate, Δ-cis-α-[Co(SS-EBP)(en)] ClO₄· 2H₂O, was determined from three-dimensional X-ray diffractometer data. The complex crystallizes in the orthorhombic system, space group P2₁2₁2₁ with a = 7.879(4) Å, b = 13.738(9) Å, c = 19.445(2) Å, V = 2104(2) ų. With Z = 4, the observed and calculated densities are 1.60(2) and 1.605 g cm^?3, respectively. The structure was refined by the block- diagonal least-squares technique to a final R = 0.0560 for 1604 observed reflections. The geometry about the cobalt atom is roughly octahedral with the tetradentate SS-EBP (= ethylenebis-S-prolinate ion), assuming cis-α configuration in which the complex possesses two out-of-plane amino acidate (R) rings and the backbone ethylenediamine (E) ring. The E ring conformation is δ. On the other hand, the R rings have λ conformation as well as the en ring. Δ-R_NR_N?(δ_E  λ_R1  λ_R2)(λ_en)-cis-α-[Co(SS-EBP)(en)]⁺ is one of two possible isomers of this compound which have been isolated and whose absolute configurations have been tentatively assigned by spectroscopy. The crystal and molecular structure determination confirms these assignments.