Substrate binding site of microsomal cytochrome P-450 directly faces membrane lipids

Cytochrome P-450, purified from liver microsomes of phenobarbital-treated rabbits, was incorporated into dimyristoylphosphatidylcholine liposomes. The binding of benzphetamine to the liposome-bound cytochrome P-450 was examined by measuring the benzphetamine-induced spectral change at various temperatures. The van't Hoff plot of the apparent spectral dissociation constant showed a distinct break at the temperature of phase transition of the synthetic lipid. On the other hand, no such break was observed for benzphetamine binding to microsomal bound cytochrome P-450. These results suggest that the substrate binding site of cytochrome P-450 is embedded in the apolar interior of phospholipid bilayer membranes.     

Specific visualization of tubulin-containing structures in tissue culture cells by immunofluorescence. Cytoplasmic microtubules, vinblastine-induced paracrystals, and mitotic figures.

Antibody against tubulin from the outer doublets of sea urchin sperm flagella reacts with tubulin-containing structures in mammalian cells. Thus cytoplasmic microtubules, vinblastine-induced paracrystals and the full spectrum of mitotic figures can be visualized by immunofluorescence. These results show that the tubulin structure has been highly conserved during evolution.     

Preparation and crystal structure of manganese(II) isothiocyanate tetrahydrate

Crystals of Mn(NCS)₂·4H₂O were isolated from an aqueous solution obtained by mixing solutions of barium thiocyanate and manganese(II) sulphate tetrahydrate. The crystals are monoclinic with a = 7.827(7), b = 9.208(1), c = 7.456(5) Å, β = 112.57(5)°, space group P2₁/c. The structure consists of discrete centrosymmetric trans-[Mn(NCS)₂(H₂O)₄] octahedra linked by hydrogen bonds.     

Morphogenesis of bacteriophage lambda deletion mutants. II. Escherichia coli mutants which prevent maturation of short genomes.

We have isolated mutants of Escherichia coli which severely reduce the growth of bacteriophage lambda carrying the b221 deletion. Some of the bacterial strains also cause a moderate reduction in the growth of wild-type phage. In the mutant hosts tested, the growth of λb221 is restored by chromosomal alterations producing a non-specific increase in genome length. Thus the defect in growth can be attributed to the physical size of the genome, rather than a genetic effect of the b221 deletion. Our experiments show that the failure to grow results from a block to head morphogenesis and that growth can be restored by mutations in at least two phage head genes. In the accompanying paper we have shown that even in the normal bacterium, the process of packing and cutting the λb221 genome is perturbed as a result of its small size. The block to morphogenesis in the bacterial mutant we have studied most extensively appears to result from an enhancement of the same effect. The experiments described support the hypothesis that there is host participation in the cutting of encapsulated lambda DNA, although it is not yet clear if this involves the direct participation of a host gene product.     

Morphogenesis of bacteriophage lambda deletion mutants. I. Abnormal head-related structures produced in normal Escherichia coli.

Late in the morphogenesis of bacteriophage lambda, DNA condenses into the nascent head and is cut from a concatemeric replicative intermediate by a nucleolytic function, Ter, acting at specific sites, called cos. As a result of this process, heads of lambda deletion mutants contain less DNA than those of the wild-type phage. It has been reported that phage with very large deletions (22% of the genome or more) grow poorly but that normal growth can be restored by the non-specific addition of DNA to the genome. This finding implies that DNA content may exert a physical effect on some stage of head assembly.We have investigated the effects of two long deletions, b221 and tdel33, on head assembly. Bacteria infected with the mutants were lysed with non-ionic detergent under conditions favoring stabilization of labile structures containing condensed DNA. It has proved possible to isolate two aberrant head-related structures produced by the deletion mutants. One of these (“overfilled heads”) contains DNA which is longer than the deletion mutant genome and is about the same size as that found in wild-type heads. These structures appear to be unable to attach tails. The second type of structure (“incompletely filled heads”) contains a short piece of DNA, 40% of the length of the mutant genome. The incompletely filled heads are found both with and without attached tails. Both of these abnormal structures are initially attached to the replicating DNA but are released by treatment with DNAase. The nature of these abnormal structures indicates that very small genomes affect a late stage of head morphogenesis, after the DNA is complexed with a capsid of normal size. The results presented suggest that underfilling of the capsid interferes with the ability of the Ter function to properly cleave cos.     

Growth-dependent regulation in production and utilization of acetylated ribosomal protein L7.

The relative levels of protein L12 and its α-N-acetylated form L7 in ribosomes of Escherichia coli have previously been shown to markedly vary during the growth cycle. The present labeling study shows preferential utilization of L12 in early logarithmic phase and of L7 in late logarithmic phase. Both forms are, however, simultaneously used throughout the growth cycle. After assembly into ribosomes, L7 and L12 are conserved without net interconversion. It is therefore concluded that the variation in L12 to L7 ratio takes place through changes in the relative flow of L7 and L12 species into ribosome assembly rather than by modification in pre-existing ribosomes. During this study, we have also measured the surprisingly large difference in the binding of Coomassie Blue to these proteins.     

Synthesis and crystal and molecular structure of a methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate complex

Bis-Methyl N,N-diethylcarbamylmethylenephosphonato dysprosium thiocyanate, Dy[O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂]₂(NCS) was prepared from the combination of ethanolic solutions of Dy(NCS)₃·xH₂O and (CH₃O)₂P(O)CH₂C(O)N(C₂H₅)₂. The complex was characterized by infrared and NMR spectroscopy, and single crystal X-ray diffraction methods. The crystal structure was determined at 25 °C from 3727 independent reflections by using a standard automated diffractometer. The complex was found to crystallize in the monoclinic space group P2₁/c with a = 13.282(4) Å, b = 19.168(5) Å, c = 9.648(2) Å, β = 90.09(2)°, Z = 4, V = 2456.4 ų and ?_cald = 1.72 g cm^?3. The structure was solved by standard heavy atom techniques, and blocked least-squares refinement converged with R_f = 4.7% and R_wF = 4.9%. The Dy atom is seven coordinate and bonded in a bidentate fashion to two anionic phosphonate ligands [O₂P(OCH₃)CH₂C(O)N(C₂H₅)₂^?] through the carbonyl oxygen atoms and one of two phosphonate oxygen atoms. In addition, each Dy atom is coordinated to two phosphonate oxygen atoms from two neighboring complexes and to the nitrogen atom of a thiocyanate ion. This coordination scheme gives rise to a two-dimensional polymeric structure. Some important bond distances include DyNCS 2.433(8) Å, DyO(carbonyl)_avg 2.39(2) Å, DyO(equat. phosphoryl)_avg 2.303(8) Å, DyO(axial phosphoryl)_avg 2.25(2), PO(phosphoryl)_avg 1.493(3) Å and CO(carbonyl)_avg 1.25(1) Å.     

The preparation and crystal structure analysis of a 2:1 complex between L-lysine and copper(II) chloride

The crystal structure of bis(L-lysine)Cu(II) chloride dihydrate has been determined by X-ray analysis. The complex crystallizes in the monoclinic space group P2₁, with cell dimensions a = 5.189(1), b = 16.988(3), c = 11.482(2) Å, β = 93.57(1)°. The position of the Cu atom was found from a Patterson synthesis, the remaining atoms were located with DIRDIF. The structure was refined by least-squares to R = 0.060 and R_w = 0.065 for 2637 observed reflections. The copper(II) atom has an essentially square planar coordination with the two lysine molecules chelated via the carboxy oxygen and the α-amino nitrogen. However the two chlorine atoms form weak interactions with the metal to complete a strongly tetragonally elongated six-fold coordination. The two aliphatic chains have rather different geometries and are extended in a zig-zag mode. Extensive hydrogen bonding links the complex and the water molecules together.     

The crystal and molecular structure of diethylenetriammonium hexachloro-antimonate(III)

A compound of the type [DenH₃]SbCl₆ (DenH₃ = diethylenetriammonium cation) was prepared and characterized by means of structural and vibrational measurements. The structure consists of monomeric SbCl₆^3? anions and triprotonated diethylenetriam-monium cations. The SbCl₆^3? anion has a strongly distorted octahedral geometry, presenting three short (2.415–2.495 Å) and three long (2.836–3.114 Å) SbCl bonds. The presence of multiple hydrogen bonds, mainly involving the counterion and the three long-bonded chlorine atoms, is considered to be responsible for the octahedral distortion. Vibrational properties of the complex are discussed in the light of its known crystal structure.     

Synthesis and characterization of nitroimidazole complexes of platinum and palladium and the crystal and molecular structure of trans-dichlorobis(misonidazole)platinum(II)

The synthesis and properties of some nitroimidazole complexes of platinum and palladium starting from the MCl₄^2- salts are described. Both 5-NO₂-imidazole and metronidazole give cis-[MCl₂L₂] complexes whereas trans-[MCl₂L₂] is obtained for 2-NO₂-imidazole and misonidazole. The crystal structure of trans-dichlorobis(misonidazole)platinum(II) was determined by three-dimensional X-ray methods. The compound crystallized in space group P2₁/c in discrete monomeric units with a = 11.303(5), b = 13.002(5) and c = 8.125(3) Å, B = 91.39(3)°, Z = 2 and the observed and calculated densities are 1.83 and 1.859 respectively. The final full-matrix least-squares refinement gave values of R₁ = 0.037 and R₂ = 0.045 for 142 variables. The complex is square-planar with Pt-Cl and Pt-N distances of 2.294(3) and 2.016(9) Å respectively. The mean plane of the misonidazole ring is twisted 56° with respect to the PtCl₂L₂ square plane and the Cl-Pt-N angles are 89.4(3) and 90.6(3)°; the nitro group also lies out of the plane of the misonidazole ring. The closest nonbonded contact between non-hydrogen atoms in the unit cells is 2.80 Å suggesting hydrogen bonding between the hydroxyl proton and the ether oxygen in the misonidazole side-chain, i.e. O-H?O. Aspects of the chemistry of these species in relation to their biological activity are discussed.     

Interaction of metal ions with humic-like models. Part 5. The crystal and molecular structure of diaquabis(2,6-dihydroxybenzoato)-dioxouranium(VI) octahydrate

The crystal and molecular structure of the complex [UO₂(DHB)₂(H₂O)₂]·8H₂O (DHB = 2,6-di- hydroxybenzoato) has been determined from single- crystal X-ray analysis and refined to a final R value of 0.033 for 3620 observed reflections. The complex crystallizes in the monoclinic system, space group C2/m, with a = 6.704(3), b = 20.171(6), c = 9.454(4) Å and Z = 2. The coordination about the uranyl group, which is linear, involves two bidentate carboxylate groups and two water molecules in trans positions giving rise to an irregular hexagonal bipyramid. Intra- molecular hydrogen bonds between phenolic and carboxylate groups forming six-membered rings allow the molecule to be nearly planar. Spectroscopic (IR, NMR and electronic absorption) data and thermal properties of the compound are also reported.     

Copper(II) halide complexes of 2-aminobenzophenone. Crystal and molecular structure of bis(2-aminobenzophenone)dichlorocopper(II)

The complexes CuX₂L₂ (X = Cl, Br; L = 2-aminobenzophenone) were prepared and characterized by means of magnetic and spectroscopic measurements. For the Cl compound the crystal structure was also determined. Crystals are triclinic, space group P$\text{1}$, with a = 13.397(3), b = 10.752(2), c = 9.205(2) Å, α = 72.26(1)°, β = 91.58(1)°, γ = 106.86(1)°, and Z = 2. The structure was solved by the heavy-atom method and refined by least-squares calculations to R = 0.034 for 2581 counter data. It consists of discrete CuX₂L₂ monomers showing distorted trigonal bipyramidal coordination geometry about the copper ion. The amino nitrogens are axial ligands, with the equatorial positions occupied by two chlorine atoms and a carbonyl oxygen from one L molecule acting as a bidentate ligand. Infrared and ligand field spectroscopies and magnetic measurements, interpreted on the basis of the known crystal structure, also suggest a similar structure for the related Br compound.     

The influence of phospholipid polar groups on gramicidin channels

The influence of well-defined changes in the polar part of phospholipid molecules on the properties of black lipid membranes was studied using a series of phospholipids with identical hydrocarbon chains, but systematically changed polar groups. The hydrocarbon tails of the lipids under study were composed of 1,2-dipentadecylmethylidene glycerol. The polar parts differed in the degree of $\text{N-}\text{methylation}$ and comprised phosphocholine, $\text{-N,N-}\text{dimethylethanolamine}$, $\text{-N-}\text{methylethanolamine}$ and ethanolamine. Stable black lipid membranes could be formed with the solvents octane, decane, dodecane, tetradecane and hexadecane. The properties of gramicidin-induced single ionic channels changed systematically in membranes from the phosphatidylcholine to the phosphatidylethanolamine analogue, as indicated by an increase in the amplitude A of the unit conductance step and a decrease in the average channel life-time or duration τ. The series of τ-values was opposite to that expected from hydrocarbon thickness (specific capacitance). It is suggested that the surface tension γ is a relevant parameter for the prediction of τ-values.     

Crystal and molecular structure of tris(propane-1,3-diamine)nickel(II) dinitrate complex

The title compound, [Ni(1,3-pn)₃](NO₃)₂, crystallizes in the orthorhombic space group Pbca with eight formula units in a cell of dimensions a = 17.146(8), b = 14.364(5) and c = 15.054(7). The structure was solved by the heavy-atom method and refined by least-squares calculations to R = 0.053 for 1439 counter data. It consists of discrete, slightly distorted octahedral [Ni(1,3-pn)₃]²⁺ cations and NO₃^? anions. One of the three six-membered chelate rings show a pronounced flattening unusual chair conformation. Magnetic and spectroscopic data agree to a lower stability of six-membered chelate rings, compared to five-membered chelate ones.     

X-ray crystal structure determinations of two thiourea tin(II) complexes: Diacetatobis(thiourea)tin(II) and ditin(II)tetrabromopenta(thiourea)dihydrate

The crystal structures of diacetatobis(thiourea)tin(II) (I) and ditin(II)tetrabromopenta(thiourea)dihydrate (II) have been determined by X-ray diffraction analysis. The compound I crystallizes in the monoclinic space group Pc with a = 11.932(6), b = 10.937(5), c = 21.919(8) Å, β = 96.5(1), Z = 8. The compound II crystallizes in the orthorhombic space group Pnma with a = 27.83(3), b = 16.13(4), c = 6.11(6) Å, Z = 4. In compound I the tin atom has a square pyramidal environment. It is bonded to two thiourea sulphur atoms and to two carboxylate oxygens. In the compound II there are two tin sites both with trigonal pyramidal coordination. The ¹¹⁹Sn Mössbauer data for thiourea tin(II) compounds are discussed, in terms of their crystal structures.     

Chromium(III) complexes and their relationship to the glucose tolerance factor. Part II. Structure and biological activity of amino acid complexes

A number of octahedral chromium complexes with amino acids are ligands have been prepared and their structures assigned on the basis of their chromatographic and spectral properties. These include complexes with the general structure Cr(AA)₂(H₂O)₂ where the amino acids glycine, glutamic acid and glutamine act as bidentate ligands. The analogous compound with cysteine as ligand is stable at low pH, but at high pH a terdentate cysteine complex, Cr(cysteine)₂^?, is formed. These complexes, as well as a solution of monodentate glycine aquo complexes, and Cr-nicotinic acid-glycine and Cr-nicotinic acid-cysteine complexes of undetermined structure, have been assayed for glucose tolerance factor activity using a yeast assay. Only Cr(glutamine)₂- (H₂O)₂⁺, Cr-nicotinic acid-glycine and the mixture of complexes Cr(glycine)_n(H₂O)_6-n⁺³ showed significant activity. It is proposed that a trans arrangement of the non-coordinated nitrogen atoms in the ligands of these complexes can mimic the structural features of the glucose tolerance factor which are essential for biological activity.     

Structure of the complex formed by bovine trypsin and bovine pancreatic trypsin inhibitor. Crystal structure determination and stereochemistry of the contact region

The structure of the complex of bovine trypsin and bovine pancreatic trypsin inhibitor has been determined by crystal structure analysis at 2.8 Å resolution. The structure is closely similar to the model predicted from the structures of the components. The complex is a tetrahedral adduct with a covalent bond between the carbonyl carbon of Lys-15I of the inhibitor and the γ-oxygen of Ser-195 of the enzyme. The imidazole of His-57 is hydrogen-bonded to Asp-102 and the bound seryl γ-oxygen in accord with the histidine being charged. The negatively charged carbonyl oxygen of Lys-15I forms two hydrogen bonds with the amide nitrogens of Gly-193 and Ser-195. Protonation of the leaving group N-H of Ala-16I to form an acyl-complex requires a conformational change of the imidazole of His-57. The tetrahedral adduct is further stabilized by hydrogen bonds between groups at the leaving group side and inhibitor and enzyme, which would be weakened in the acyl-enzyme. The kinetic data of inhibitor-enzyme interaction are reconciled with the structural model, and relations between enzyme-inhibitor interaction and productive enzyme-substrate interaction are proposed.