Structure of 7S seed globulin from Phaseolus vulgaris L. in solution

The structure of the 7S globulin from Phaseoulus vulgaris L in dilatue solutions has been studied by small angle X-ray scattering (SAXS), by quasi-elastic light scattering (Q ELS), by circular dichroism spectroscopy (c.d.), and by precise density measurements. The molar mass, the radius of gyration, the volume, the maximum dimension and the diffusion coefficient were determined as M = 1.45 × 10⁵ g mol⁻¹, R_G = 4.05 nm, V = 300- nm³, L = 13.0 nm and D_20,w⁰ = 4.5 × 10⁻⁷ cm² s⁻¹, respectively. The molecule has an asymmetrical shape with the dimensions 12.5 × 12.5 × 3.75 nm. The secondary structure of the 7S globulin is characterized by a small portion of -helical structure (14%) and a marked content of β-structure (18%).     

Dependence of Lipase Activity on Water Content and Enzyme Concentration in Reverse Micelles

The activity of Candida rugosa lipase (EC 3.1.1.3) in reverse micelles has been measured at various concentrations of water and enzyme with the aim of answering the question, why is the enzyme activity affected by the molar ratio of water to surfactant (w₀ = [H₂O]/[Surfactant])? In the low range of water content (below w₀ ≈ 6), the activity increases with increasing water content, indicating the requirement of a minimum amount of water for the full expression of enzymatic activity. The minimal w₀-value for obtaining maximal activity depends on the enzyme concentration: The higher the enzyme concentration, the higher w_{0, max}. In addition, it was found that, at least for the case of Candida rugosa lipase, the measured dependence of enzyme activity on w₀ does not represent a true chemical equilibrium. Changing the w₀-value during the reaction does not change the activity as expected on the basis of the w₀-activity profile obtained for single w₀ point measurements. All these observations, however, cannot be directly generalized to all enzymes in reverse micelles, due to the peculiarity of lipase. In particular, the enzyme seems to inactivate irreversibly during the solubilization process.     

Assessment of the validity of the Adams and Fujita approximation for the higher oligomers of human spectrin

Analysing the self-association behaviour of human erythrocyte spectrin is complicated by a large degree of nonideality. Adams and Fujita [1] proposed that, as a first order approximation, the logarithm of the activity coefficient of the protomer of a self-associating system can be considered to be linearly dependent on the total concentration of the protein, and that the same second virial coefficient could be considered to apply to all species. As a consequence of the Adams and Fujita approximation, the apparent equilibrium constant is equal to the thermodynamic equilibrium constant. The equilibrium concentrations at 30°C of each oligomer spectrin species up to the 14-mer were determined after electrophoresis at low temperature. An apparent equilibrium constant for forming tetramer (K_2,4) of (1.2 ± 0.1) × 10⁶ l/mol was obtained, a value of (9.4 ± 0.7) × 10⁴ l/mol was obtained for K_4,6 and for all reactions forming oligomers higher than the hexamer an average approximate value of (2.7 ± 0.4) × 10⁵ l/mol was obtained. The apparent equilibrium constants for the formation of all oligomer species of spectrin up to the tetrakaidecamer (14-mer) remain relatively independent of total spectrin concentration, and indicate that within the precision of the measurements a single virial coefficient is sufficient to account for the nonideality of spectrin self-association over the range 2–42 g/l, thus further justifying the use of the Adams and Fujita approximation for this protein over this concentration range.     

Equilibrium and structure of thallium(III)–ethylenediamine complexes in pyridine solution and in solid

The formation of three [Tl(en)_n]³⁺ complexes (n=1–3) in a pyridine solvent has been established by means of ²⁰⁵Tl and ¹H NMR. Their stepwise stability constants based on concentrations, K_n=[Tl(en)_n ³⁺]/{[Tl(en)_n−1 ³⁺]·[en]}, at 298 K in 0.5 M NaClO₄ ionic medium in pyridine, were calculated from ²⁰⁵Tl NMR integrals: log K₁=7.6±0.7; log K₂=5.2±0.5 and log K₃=2.64±0.05. Linear correlation between both the ²⁰⁵Tl NMR shifts and spin–spin coupling ²⁰⁵Tl–¹H versus the stability constants has been found and discussed. A single crystal with the composition [Tl(en)₃](ClO₄)₃ was synthesized and its structure determined by X-ray diffraction. The Tl³⁺ ion is coordinated by three ethylenediamine ligands via six N-donor atoms in a distorted octahedral fashion.     

Screening the physical properties of novel Pseudomonas exopolysaccharides by HPSEC with multi-angle light scattering and viscosity detection

The physical properties of three novel acidic exopolysaccharides obtained from P. marginalis types A, B and C, one from P. ‘gingen’, one from P. andropogenis and one from P. fluorescens have been partially characterized. These EPSs were chromatographed on three serially placed SE Shodex OH pak columns covering a molar mass range for pullulans from about 4 × 10⁷ to 1 × 10³. The mobile phase was 0.05 M NaNO₃. Physical measurements were performed on about 30 mg of sample for each EPS. The weight average molar mass of these EPSs ranged from about 0.71 to 2.85 × 10⁶, the weight average intrinsic viscosity from 7.15 to 35.3 dl/ g and the radius of gyration from 62 to 123nm. The polydispersities of these EPSs ranged from 1.01 to 1.37. The large molar mass, size and viscosities of these EPSs may indicate that they have potential for use as thickeners, stabilizers, emulsifiers, and gelling agents in the food and non-food industries.     

Relationship between cyprid energy reserves and metamorphosis in the barnacle Balanus amphitrite Darwin (Cirripedia; Thoracica)

Nauplii batch cultures of Balanus amphitrite were reared with four different diatoms (Skeletonema costatum, Thalassiosira pseudonana, Chaetoceros gracilis, silicate-limited C. gracilis) at three different cells concentrations: 1×10⁵, 5×10⁵, and 1×10⁶ cells ml⁻¹. The cyprid energy reserves were quantified as the ratio of triacylglycerols (TAG) to DNA. Energy reserves of larvae fed on different diatoms at a concentration of 1×10⁶ cells ml⁻¹ were ranked in the order: silicate-limited C. gracilis>C. gracilis>T. pseudonana>S. costatum. There was a significant linear relationship between the TAG content of the diet and cyprid energy reserves. The effect of cyprid energy reserves on metamorphosis to polystyrene surface in the presence and the absence of conspecific settlement factor (SF) was studied after 12, 24, and 48 h of incubation. A strong positive correlation between energy reserves and percent metamorphosis was observed in the absence of SF (r_{12 h}=0.88, r_{24 h}=0.82, r_{48 h}=0.68, P<0.05). A weak positive correlation was observed in the presence of SF (r_{12 h}=0.43, r_{24 h}=0.48, r_{48 h}=0.50, P<0.05). In both treatments, more than 80% of the cyprids with high energy reserves metamorphosed within 24 h. In contrast, a high proportion of cyprids with low energy reserves metamorphosed in response to SF in 24 h. Our results indicate that discriminatory metamorphic behavior of cyprids is closely linked to their TAG/DNA ratio, a proxy for energy reserve.     

A new purification procedure and molecular properties of Pseudomonas cytochrome oxidase

A procedure has been developed for purification of the cytochrome oxidase from Pseudomonas aeruginosa (EC 1.9.3.2) using DEAE- and CM-cellulose chromatography, gel filtration and crystallization. The final preparation was found to be homogeneous according to ultracentrifugal and disc electrophoretic criteria. The crystalline preparation also exhibited nitrite reductase activity. The spectrum of the enzyme characterizes it as cytochrome cd. At 280 nm E^{1 %}_{1 cm} was 18.5 after dry weight analysis.

The molecular weight of the cytochrome oxidase was calculated to be 119000 based on a sedimentation coefficient s° _20,w = 7.36 S, diffusion coefficient D _20,w = 5.36×10⁻⁷ cm²×s⁻¹ and partial specific volume of 0.72 ml/g. The iron content of the enzyme (0.166 %) indicates that this entity contains four iron atoms per molecule. Succinylation of the enzyme produced two probably identical subunits containing both hemes c and d, having a sedimentation coefficient s° _20,w = 4.30 S and an approximate molecular weight of 65000. In dodecylsulphate-acrylamide gel electrophoresis the cytochrome oxidase also dissociates into two subunits with molecular weight of 63000.     

PATHWAYS OF INCORPORATION OF FATTY ACID INTO GLYCEROLIPIDS OF THE MURINE PERIPHERAL NERVOUS SYSTEM IN VIVO: ALTERATIONS IN THE DYSMYELINATING MUTANT TREMBLER MOUSE

In vivo glycerolipid metabolism was studied in sciatic nerves of normal and Trembler mice. The results showed that two kinetically independent pathways were implicated in the labeling of diacylglycerophospholipids from [³H]palmitate: the Kennedy pathway and a ‘direct acylation’ pathway. In normal nerves, 45% of the glycerophospholipids were labeled, with a rate constant k₃ = 3.9 × 10⁻³ min⁻¹, from phosphatidic acid and diacylglycerol intermediates, themselves formed with a rate constant of k₁ = 0.24 min⁻¹ from a free ³H-fatty acid pool, FFA₁, that represents 45% of the total injected label. The remaining 55% of the glycerophospholipids were labeled from a kinetically distinct free ³H-fatty acid pool, FFA₂, with a rate constant of k₄ = 9.8 × 10⁻², via a process that does not implicate a detectably labeled metabolic intermediate (‘direct acylation’). Glycerophospholipid labeling via the Kennedy pathway in the Trembler mouse sciatic nerves was reduced to 75% of the normal level, while labeling via the ‘direct acylation’ pathway was increased 1.4-fold. The values of the rate constants for free ³H-fatty acid utilisation (k₁ and k₄) were both increased about 2.5-fold, while that of glycerophospholipid formation from diacylglycerol (k₃) was close to normal. Copyright © 1996 Elsevier Science Ltd     

Isolation and characterization of soluble sulfated polysaccharide from the red seaweed Gracilaria cornea

The composition, structure and rheological properties of a soluble sulfated polysaccharide from Gracilaria cornea (Brazilian red marine alga) were investigated. Agarocolloid yield, intrinsic viscosity, monosaccharide composition, sulfate and cation content as well as molecular weight were determined. The main polysaccharide components were 3,6-anhydrogalactose (24.7%) and galactose (64.6%). In addition, minor components such as 6-O-methyl-galactose (8.5%), glucose (1.5%), xylose (0.7%) and sulfated groups (4.8%) were detected. Comparison between sulfate contents determined by Fourier transform IR (FT-IR) spectroscopy and microelemental analysis was made. Data from ¹³C NMR and FT-IR provided evidence of sulfation in C-4 and C-6 of galactose. Sodium, calcium, magnesium and potassium cations were detected in the agarocolloid. The intrinsic viscosities were lower than typical values for agar in the same experimental conditions. No gelation in 1.5, 2.0 and 3.0% (w/v) aqueous solution was observed, even by cooling up to 4 °C. Gel permeation chromatography indicated two major polysaccharide fractions of M_pk 7.4×10⁴ and 1.8×10⁴ g/mol and a minor fraction of M_pk 2.1×10⁶ g/mol, probably a protein–polysaccharide complex.     

The radiosensitivity of spermatogonial stem cells in C3H/101 F1 hybrid mice

The radiosensitivity of spermatogonial stem cells of C3H/HeH × 101/H F₁ hybrid mice was determined by counting undifferentiated spermatogonia at 10 days after X-irradiation. During the spermatogenic cycle, differences in radiosensitivity were found, which were correlated with the proliferative activity of the spermatogonial stem cells. In stage VIII_irr, during quiescence, the spermatogonial stem cells were most radiosensitive with a D₀ of 1.4 Gy. In stages XI_irr−V_irr, when the cells were proliferatively active, the D₀ was about 2.6 Gy. Based on the D₀ values for sensitive and resistant spermatogonia and on the D₀ for the total population, a ratio of 45:55% of sensitive to resistant spermatogonial stem cells was estimated for cell killing.

When the present data were compared with data on translocation induction obtained in mice of the same genotype, a close fit was obtained when the translocation yield (Y; in % abnormal cells) after a radiation dose D was described by Y = e^τD, with τ = 1 for the sensitive and τ = 0.1 for the resistant spermatogonial stem cells, with a maximal e^τD of 100.     

Ruthenium complex catalyzed polymerization of OH or COOH group containing alkynes to give functionalized poly(acetylene)s

The ruthenium(III) complex [(Cp*)RuCl₂]₂ (Cp*=permethylcyclopentadienyl) catalyzes polymerization of propiolic acid to give a mixture of poly(propiolic acid), [---CH=C(COOH)---]_n (1), and cyclic trimers, 1,2,4- and 1,3,5- benzenetricarboxylic acids. GPC analysis shows MN and MW values of the polymer of 4.0 × 10³ and 4.3 × 10³, respectively. Reaction of propiolic acid in the presence of the Ru(II) complex, (Cp*)RuCI(L) (L=1,5-cyclooctadiene and norbornadiene), gives the cyclic trimers rather than 1. [(Cp*)RuCl₂]₂ catalyzes polymerization of acetylenedicarboxylic acid and of propargyl alcohol to give the corresponding poly(acetylene) derivatives, [---C(COOH)=C(COOH)---]_n (2) and [---CH=C(CH₂OH)---]_n (3), respectively. Polymerization of ethyl propiolate, 2-butyn-1,4-diol, phenylacetylene and (trimethylsilyl)acetylene using [(Cp*)RuCl₂]₂ gives the corresponding polymers [---CH=C(COOEt)---]_n (4), [---C(CH₂OH)=C(CH₂OH)---]_n (5), [---CH=CPh---]_n (6) and [---CH=C(SiMe₃)---]_n (7) in low yields.     

Kinetics and equilibria of Ga(III)---thiocyanate complex formation. Mechanism of ligand substitution reactions of Ga(III) in aqueous solution

The kinetics and equilibria of complex formation by Ga(III) with NCS⁻ in aqueous solution have been measured over a range of acidities and temperatures, the contributing paths to the reaction resolved, and their rate constants and activation parameters determined. The hydrolysis equilibria required to carry out this resolution of kinetic behaviour have also been measured.

Unlike the other reported complexation reactions of Ga(III) in aqueous solution, the separate reaction pathways can be assigned with no ambiguity. At 25 °C and ionic strength 0.5 M, the observed forward rate constant for the complex formation is described by {k₁ + k₂K_1h/[H⁺] + k₃K_1hK_2h/[H⁺]²} M⁻¹ s⁻¹. For these conditions, the first and second successive hydrolysis constants of Ga(H₂O)₆³⁺ are given by pK_1h = 3.69 ± 0.01 and pK_2h = 3.74 ± 0.04. The rate constants corresponding to the reactions of the species Ga(H₂O)₆³⁺, Ga(H₂O)₅(OH)²⁺ and Ga(H₂O)₄(OH)₂⁺ with NCS⁻ are k₁ = 57 ± 4 M^{−1 −1}, k₂ = (1.08 ± 0.01) × 10⁵ M⁻¹ s⁻¹ and k₃ = 3 × 10⁶ M⁻¹ s⁻¹ respectively. The complexation equilibrium quotient [GaNCS²⁺]/([Ga³⁺][NCS⁻]) has been independently determined by spectrophotometric titration to be 20.8 ± 0.3 M⁻¹ at 25 °C and ionic strength 0.5 M.

These kinetic results lead to an interpretation of the data, and a reinterpretation of other data for aquo-Ga(III) complex formation kinetics from the literature which support the assignment of a dissociative interchange mechanism for these reactions rather than the associative activation mode sometimes proposed.     

Biochemical and biophysical studies on cytochrome aa3 VIII. Effect of cyanide on the catalytic activity

1. 1. Cyanide inhibits the catalytic activity of cytochrome aa₃ in both polarographic and spectrophotometric assay systems with an apparent velocity constant of 4·10³ M⁻¹·s⁻¹ and a K_i that varies from 0.1 to 1.0 μM at 22 °C, pH 7·3.

2. 2. When cyanide is added to the ascorbate-cytochrome c-cytochromeaa₃−O₂ system a biphasic reduction of cytochrome c occurs corresponding to an initial K_i of 0.8 μM and a final K_i of about 0.1 μM for the cytochrome aa₃−cyanide reaction.

3. 3. The inhibited species (a²+a₃³⁺HCN) is formed when a²⁺a₃³⁺ reacts with HCN, when a²⁺a₃²⁺HCN reacts with oxygen, or when a³⁺a₃³⁺HCN (cyano-cytochrome aa₃) is reduced. Cyanide dissociates from a²⁺a₃³⁺HCN at a rate of 2·10⁻³ s⁻¹ at 22 °C, pH 7.3.

4. 4. The results are interpreted in terms of a scheme in which one mole of cyanide binds more tightly and more rapidly to a²⁺a₃³⁺ than to a³⁺a₃³⁺.

The vibrational spectrum of TpRhH2(H2): a computational and inelastic neutron scattering study

We report extensive density functional theory studies of the structures and vibrational frequencies of Tp^3,5-MeRhH₂(H₂) in its ground and various transition states as well as the first direct comparison of observed and calculated inelastic neutron scattering (INS) vibrational spectra on this type of compound. Geometry optimizations produced canted η²-dihydrogen dihydride local minima of C₁ symmetry; with HH distances for the C₁ minimum energy structure of 0.842 and 0.898 Å and barriers to rotation of 0.34 and 0.50 kcal mol⁻¹, respectively for B3LYP/BS1 and BP86/BS1 calculations of Tp^3,5-MeRhH₂(H₂). The latter results from one transition state rotated approximately 60° away (a second lower energy transition state which is a few hundreds of a kcal mol⁻¹ above the C₁ MIN is rotated approximately 30° away). With these calculated d(HH) values for the C₁ MIN the previously reported experimental data on the rotation of the dihydrogen ligand yields an experimental barrier to rotation of 1 kcal mol⁻¹ and places the torsional transition at 200 cm⁻¹ in the INS spectrum. Optimization of the Rh structure, that is analogous to the related Ir(V) C_s minimum found for TpIrH₄, generates a high-energy (>4 cal mol⁻¹) C_s transition state TpRh^IIIH₄ structure with an η³-H₃ ⁻ ligand. This transition state (C_s TSE) exchanges the hydrogen in the mirror plane between two chiral C₁ MIN structures. Comparisons between observed and computed INS spectra suggests that the experimental INS spectrum be viewed as resulting from a quantum-averaged ground state encompassing at least two of the low energy structures found in our calculations.     

Anisotropy in hard dental tissues

The critical angle reflection technique was used to determine longitudinal and shear sonic velocity components in the exposed surface of bovine incisors along the tooth axis and perpendicular to it. By grinding a flat on the tooth surface successive layers were exposed and the velocity components measured. Plots of the velocity variation with depth were prepared which show some variation in the enamel, much less in the dentine and a sharp drop at the dentino-enamel junction. Strong evidence of anisotropy is demonstrated, especially in enamel.

The longitudinal velocity component is larger than previous values for measurements through these hard tissues. Hydroxyapatite and bone models assuming hexagonal symmetry indicate that the surface velocity should be the smaller component. The Katz hexagonally symmetrical bone model shows a significant dip in the velocity along the 45° propagation direction. If it is assumed that prior measurements correspond to the 45° rather than the c-axis direction, a set of elastic constants can be calculated which are an estimate for enamel and dentine. These resemble the Katz bone model.

Enamel C₁₁ 115, C₁₂ 42·4, C₁₃ 30, ₃₃ 125, C₄₄ 22·8

Dentine C₁₁ 37, C₁₂ 16·6, C₁₃ 8·7, C₃₃ 39, C₄₄ 5·7

Katz bone model C₁₁ 31, C₁₂ 14·7, C₁₃ 11·3, C₃₃ 33, C₄₄ 6·2

(all × 10⁹N/m²)

Poisson's ratio for enamel is estimated to be 0·28 and for dentine 0·32.     

Characterization of gliadin-galactomannan incubation mixtures by analytical ultracentrifugation—Part I. Sedimentation velocity

The aim of this work is to examine the possible interaction and extent thereof of the polysaccharide galactomannan (GAL) with the cereal protein gliadin (GLI) and a peptic-tryptic degraded gliadin (PT-GLI) by analytical ultracentrifugation. The work is part of a series of investigations into the field of coeliac disease (gluten-induced enteropathy) as gliadins are known to be toxic for patients with this disease.

The molecular integrity of the GAL and GLI preparations was first checked by sedimentation velocity and sedimentation equilibrium. Sedimentation velocity showed single boundaries indicating homogeneity and low-speed sedimentation equilibrium gave plausible apparent weight average molar masses of 180,000 g/ mol for GAL and 20,000 g/mol for GLI. PT-GLI, GLI and GAL in phosphate buffer (pH 6.5) and the incubated mixtures (stirred for 3 h at 37 °C; PT-GLI: GAL = 3.53:1, wt.wt.; GLI:GAL = 0.23 and 0.55:1, wt.wt.) were then investigated by sedimentation velocity at a temperature of 20 °C. The plots of 1/s₂₀ vs. c of GAL, PT-GLI-GAL and GLI-GAL mixtures after incubation show a significantly different shape suggesting the presence of interactions. According to the equation 1/s₂₀ = 1/s^o₂₀(1 + k_sc), values for {s^o₂₀, k_s} of {(4.02 ± (490.9 ± 28.9) ml/g, {(5.92 ± 0.24) S, (1152 ± 44) ml/g} and {(5.38 ± 0.19) S, (1141 ± 38) ml/g} for GAL and PT-GLI-GAL and GLI-GAL mixtures, respectively, were obtained. The concentration of GAL ranged from 0.75–3.0 mg/ml for GAL alone and from 0.34–1.50 mg/ml in the incubated mixtures. This apparent indication for a weak non-covalent protein-polysaccharide interaction was further supported by UV absorption spectrometry and gel filtration.     

Order and fluidity in the terminal methyl region of dipalmitoyl phosphatidylcholine multibilayers: A comparison of raman and H-NMR spectroscopy

Deuterium magnetic resonance (²H-NMR) and Raman spectroscopy are used to investigate order and fluidity at the terminal methyl position in 16-d₃, 16′-d₃ dipalmitoylphosphatidylcholine (16-d₆ DPPC) multibilayers. These methods reveal substantial motion and disorder in the gel phase, 5–10°C below the gel-liquid crystal phase transition temperature (T_m). The phase transition is sensed in the ²H-NMR spectrum as a reduction in the quadrupole splitting from 14 kHz to 3 kHz. In contrast, the Raman parameter used to characterize the CD₃ vibrations is quite insensitive to the melting process, although an analogous parameter does sense disordering at T_m at the 10 and 10′ position in 10-d₂, 10′-d₂ DPPC. The difference in the response of the NMR and Raman parameters may arise because the vibrational spectrum of the CD₃ group is inhomogenously broadened and is therefore quite sensitive to alterations in the local environment around the methyl group. In contrast, the NMR quadrupole splitting is sensitive to both local motion of the methyl group and, near Tm, to motions of the CD₂ group induced by transgauche isomerizations further up the chain. The difficulties that arise when results from different spectroscopic techniques are compared are demonstrated.     

Competitive product inhibition of aromatase by natural estrogens

In order to better understand the function of aromatase, we carried out kinetic analyses to asses the ability of natural estrogens, estrone (E₁), estradiol (E₂), 16-OHE₁, and estriol (E₃), to inhibit aromatization. Human placental microsomes (50 μg protein) were incubated for 5 min at 37°C with [1β-³H]testosterone (1.24 × 10³ dpm ³H/ng, 35–150 nM) or [1β-³H,4-¹⁴C]androstenedione (3.05 × 10³ dpm ³H/ng, ³H/¹⁴C = 19.3, 7–65 nM) as substrate in the presence of NADPH, with and without natural estrogens as putative inhibitors. Aromatase activity was assessed by tritium released to water from the 1β-position of the substrates. Natural estrogens showed competitive product inhibition against androgen aromatization. The K_i of E₁, E₂, 16-OHE₁, and E₃ for testosterone aromatization was 1.5, 2.2, 95, and 162 μM, respectively, where the K_m of aromatase was 61.8 ± 2.0 nM (n = 5) for testosterone. The K_i of E₁, E₂, 16-OHE₁, and E₃ for androstenedione aromatization was 10.6, 5.5, 252, and 1182 μM, respectively, where the K_m of aromatase was 35.4 ± 4.1 nM (n = 4) for androstenedione. These results show that estrogens inhibit the process of andrigen aromatization and indicate that natural estrogens regulate their own synthesis by the product inhibition mechanism in vivo. Since natural estrogens bind to the active site of human placental aromatase P-450 complex as competitive inhibitors, natural estrogens might be further metabolized by aromatase. This suggests that human placental estrogen 2-hydroxylase activity is catalyzed by the active site of aromatase cytochrome P-450 and also agrees with the fact that the level of catecholestrogens in maternal plasma increases during pregnancy. The relative affinities and concentration of androgens and estrogens would control estrogen and catecholestrogen biosynthesis by aromatase.     

Toxicity and mutagenicity of X-rays and [125I]dUrd or [3H]TdR incorporated in the DNA of human lymphoblast cells

We measured the toxicity and mutagenicity induced in human diploid lymphoblasts by various radiation doses of X-rays and two internal emitters. [¹²⁵I]iododeoxyuridine ([¹²⁵I]dUrd) and [³H]thymidine ([³H]TdR), incorporated into cellular DNA. [¹²⁵I]dUrd was more effective than [³H]TdR at killing cells and producing mutations to 6-thioguanine resistance (6TG^R). No ouabain-resistant mutants were induced by any of these agents. Expressing dose as total disintegrations per cell (dpc), the D₀ for cell killing for [¹²⁵I]dUrd was 28 dpc and for [³H]TdR was 385 dpc. The D₀ for X-rays was 48 rad at 37°C. The slopes of the mutation curves were approximately 75 × 10⁻⁸ 6TG^R mutants per cell per disintegration for [¹²⁵I]dUrd and 2 × 10⁻⁸ for [³H]TdR. X-Rays induced 8 × 10⁻⁸ 6TG^R mutants per cell per rad. Normalizing for survival, [¹²⁵I]dUrd remained much more mutagenic at low doses (high survival levels) than the other two agents. Treatment of the cells at either 37°C or while frozen at −70°C yielded no difference in cytotoxicity or mutation for [¹²⁵I]dUrd or [³H]TdR, whereas X-rays were 6 times less effective in killing cells at −70°C.

Assuming that incorporation was random throughout the genome, the mutagenic efficiencies of the radionuclides could be calculated by dividing the mutation rate by the level of incorporation. If the effective target size of the 6TG^R locus is 1000–3000 base pairs, then the mutagenic efficiency of [¹²⁵I]dUrd is 1.0–3.0 and of [³H]TdR is 0.02–0.06 total genomic mutations per cell per disintegration. ¹²⁵I disintegrations are known to produce localized DNA double-strand breaks. If these breaks are potentially lethal lesions, they must be repaired, since the mean lethal dose (D₀) was 28 dpc. The observations that a single dpc has a high probability of producing a mutation (mutagenic efficiency 1.0–3.0) would suggest, however, that this repair is extremely error-prone. If the breaks need not be repaired to permit survival, then lethal lesions are a subset of or are completely different from mutagenic lesions.     

Synthesis and solution behavior of the trinuclear palladium(II) unsaturated carboxylate complexes triangle-Pd3[μ-O2CC(R′) = CHMe]6 (R′ = Me, H): X-ray structure of palladium(II) tiglate (R′ = Me)

The first examples of binary palladium(II) derivatives of unsaturated carboxylic acids are reported. It was found that the interaction of Pd₃(μ-OAc)₆ with the ,β-unsaturated 1-methylcrotonic (tiglic) and crotonic acids leads to the corresponding carboxylates of composition Pd₃[μ-O₂CC(R′) = CHMe]₆, where R′ = Me (1) or H (2). The new compounds have been characterized by elemental analysis, solid and solution IR, ¹H and ¹³C NMR, and ESI mass spectrometry. The crystal structure of 1 has been determined. This molecule displays a central Pd₃ cyclic core with Pd–Pd distances of 3.093–3.171 Å. Each Pd–Pd bond is bridged by a pair of carboxylate ligands, one above and the other below the Pd₃ plane, providing a square planar coordination for each Pd atom in an approximate D_3h overall symmetry arrangement. Solution spectroscopic data show that the bridging η¹:η¹:μ₂ interaction of the carboxylates of 1 and 2 is readily displaced, with a change of the ligand to the terminal (η¹) coordination mode.