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Biomedical subjects

U Westphal

Publications and source records attributed to U Westphal.

At least 19 recordsLinked to original sources
PubMed2001

Superelectrophilic tetrakis(carbonyl)palladium(II)- and -platinum(II) undecafluorodiantimonate(V), [Pd(CO)4][Sb(2)F(11)]2 and [Pt(CO)4][Sb(2)F(11)]2: syntheses, physical and spectroscopic properties, their crystal, molecular, and extended structures, and density functional calculations: an experimental, computational, and comparative study .

The salts [M(CO)(4)][Sb(2)F(11)](2), M = Pd, Pt, are prepared by reductive carbonylation of Pd[Pd(SO(3)F)(6)], Pt(SO(3)F)(4) or PtF(6) in liquid SbF(5), or HF-SbF(5). The resulting moisture-sensitive, colorless solids are thermally stable up to 140 degrees C (M = Pd) or 200 degrees C (M = Pt). Their thermal decompositions are studied by differential scanning calorimetry (DSC). Single crystals of both salts are suitable for an X-ray diffraction study at 180 K. Both isostructural salts crystallize in the monoclinic space group P2(1)/c (No. 14). The unit cell volume of [Pt(CO)(4)][Sb(2)F(11)](2) is smaller than that of [Pd(CO)(4)][Sb(2)F(11)](2) by about 0.4%. The cations [M(CO)(4)](2+), M = Pd, Pt, are square planar with only very slight angular and out-of-plane deviations from D(4)(h)() symmetry. The interatomic distances and bond angles for both cations are essentially identical. The [Sb(2)F(11)](-) anions in [M(CO)(4)][Sb(2)F(11)](2,) M = Pd, Pt, are not symmetry-related, and both pairs differ in their Sb-F-Sb bridge angles and their dihedral angles. There are in each salt four to five secondary interionic C- -F contacts per CO group. Of these, two contacts per CO group are significantly shorter than the sum of the van der Waals radii by 0.58 - 0.37 A. In addition, structural, and spectroscopic details of recently synthesized [Rh(CO)(4)][Al(2)Cl(7)] are reported. The cations [Rh(CO)(4)](+) and [M(CO)(4)](2+), M = Pd, Pt, are characterized by IR and Raman spectroscopy. Of the 16 vibrational modes (13 observable, 3 inactive) 10 (Pd, Pt) or 9 (Rh), respectively, are found experimentally. The vibrational assignments are supported by DFT calculations, which provide in addition to band positions also intensities of IR bands and Raman signals as well as internal force constants for the cations. (13)C NMR measurements complete the characterization of the square planar metal carbonyl cations. The extensive characterization of [M(CO)(4)][Sb(2)F(11)](2), M = Pd, Pt, reported here, allows a comparison to linear and octahedral [M(CO)(n)()][Sb(2)F(11)](2) salts [M = Hg (n = 2); Fe, Ru, Os (n = 6)] and their derivatives, which permit a deeper understanding of M-CO bonding in the solid state for superelectrophilic cations with [Sb(2)F(11)](-) or [SbF(6)](-) as anions.

Journal Article↗
PubMed1983

Corticosteroid-binding globulin. A review of some recent aspects.

Among the numerous corticosteroid-binding proteins that have been demonstrated to exist throughout the vertebrates, the corticosteroid-binding globulins (CBG or transcortin) of man and guinea pig have been most thoroughly investigated. Both are glycoproteins that contain one binding site for corticosteroid hormones and other steroids. The binding forces are predominantly of a hydrophilic nature, in addition to hydrophobic interaction. Human CBG forms a reversible dimer that maintains full binding affinity and capacity. The monomeric form is composed of two electrophoretic variants that appear indistinguishable in their chemical, immunological, and steroid binding properties. Thermodynamic analysis indicates different binding mechanisms for human and cavian CBG at the lower and higher temperature range. Entrance of hydroxy groups into the steroid molecule increases the affinity to CBG; the contributions to the free energy of complex formation, resulting from individual substitutions or other alterations in the steroid molecule, are additive. Determination of binding specificity leads to a conceptual image of the steroid binding site with respect to the nature of the various binding domains.

Animals↗
PubMed1983

Steroid-protein interaction: from past to present.

In this review, the association between biologically active compounds and proteins is seen in the light of axioms expressed by Paracelsus and Paul Ehrlich long ago, and the physiological significance of the interactions is pointed out. Of the various types of proteins that form noncovalent complexes with steroid hormones, only the serum proteins will be discussed. Recent results, obtained in several laboratories, on the physicochemical properties of the human corticosteroid-binding globulin (CBG, transcortin) makes this glycoprotein perhaps the best known one among the steroid-binding serum proteins. Influence of pH on stability of the complexes, kinetics of the associations and their significance, as well as thermodynamic parameters of complex formation are being discussed. Characteristics of the binding sites are deduced from specificity studies. Influence of the entrance of hydrophilic or hydrophobic substituents into the steroid molecule illuminates the difference between typically hydrophobic binders such as the progesterone-binding globulin (PBG) of the pregnant guinea-pig and typically hydrophilic binders such as CBG. Complete elucidation of the steroid-binding proteins awaits the determination of the amino acid sequence and the X-ray crystallographic analysis of the steroid-protein complex.

Animals↗
PubMed1982

Steroid-protein interactions. Human corticosteroid-binding globulin: characterization of dimer and electrophoretic variants.

Human corticosteroid-binding globulin (CBG) forms a dimer that was isolated by gel filtration, has full binding affinity and capacity, and can be dissociated to the monomer. Monomeric CBG consists of two distinct molecular variants, which were detected by polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate. The two monomeric CBG species were separated by preparative gel electrophoresis and were found to bind cortisol, as well as progesterone, with equal affinity. They have one steroid binding site per CBG molecule. Amino acid and carbohydrate analyses are essentially the same for both of the CBG variants. Removal of sialic acid or 90% of the carbohydrate did not affect the existence of the two molecular forms. The two CBG species were isolated from each of the sera from five individual donors, indicating that the observed heterogeneity does not result from pooling genetic variants. The two species are immunologically identical. A possible explanation for the existence of the two electrophoretic variants is a difference in amidation.

Binding Sites↗
PubMed1982

Specificity and stability of guinea pig anti-progesterone antibodies.

Antibodies against progesterone were induced in guinea pigs of both sexes by injection of progesterone-y beta-hemisuccinate conjugated to bovine serum albumin (BSA) in a ratio of 16 moles of steroid per mole of protein. The concentration of antibody binding sites for progesterone of the animals studied ranged from 5 to 20 microM. The expected heterogeneity of binding affinity for progesterone was observed with two major populations apparently predominating. On bound progesterone with an average affinity greater than 2 X 10(9) M-1 and the other showed an average affinity less than or equal to 6 X 10(6) M-1. The antibodies were fond to be stable to extremes of pH and temperature in serum as well as in solutions of ammonium sulfate precipitates. The antibodies were not stable, however, in a more highly purified form. Attempts to obtain active preparations in high yield by purification beyond the ammonium sulfate step were unsuccessful. Competition studies and direct analysis with radiolabeled steroids showed the high-affinity population to be relatively specific for progesterone binding, whereas other steroids were bound according to the polarity rule indicating that the binding forces are predominantly hydrophobic.

Animals↗
PubMed1981

Steroid-protein interactions. Human corticosteroid binding globulin: some physicochemical properties and binding specificity.

Reducing agents (dithiothreitol and beta-mercaptoethanol) significantly decrease the affinity constants of the human corticosteroid-binding globulin (CBG)-cortisol complex in proportion to their concentration; the resulting Ka values are more consistent than those obtained in the absence of the reductants. The effect is reversible. The equilibrium association constants of the CBG complexes with cortisol and progesterone show a relatively broad pH maximum between pH 8 and 11. In this pH range, cortisol was found to be bound more strongly than progesterone; this relationship is reversed around pH 6. The van't Hoff plot of the temperature effect on Ka of the CBG-cortisol complex (4-41 degrees C) exhibits a nonlinear, possibly biphasic temperature dependency. The shape of the van't Hoff plot was similar in the presence of mercaptoethanol. The association of cortisol and progesterone to human CBG at 4 and 37 degrees C is enthalpy driven, compensating for the unfavorable change in entropy. Studies with 47 steroids served to elucidate the influence on binding affinity of polar and nonpolar groups and other structural alterations. The contribution of specific structural changes in the steroid molecule to the free energy of binding can be calculated from the results. Important structures for optimal binding are the 20-oxo group, a 10 beta-methyl group, and a double bond at the 4 position. A complementary image of the binding site with respect to the nature of binding at various locations is proposed.

Animals↗
PubMed1979

Purification and characterization of the corticosteroid-binding globulin of pregnant guinea pig serum.

The corticosteroid-binding globulin from guinea pig pregnancy serum was purified by the sequential use of affinity chromatography, hydroxylapatite chromatography, and gel filtration chromatography at a cumulative yield of 80%. The protein was found to be homogeneous by analytical gel electrophoresis, equilibrium sedimentation ultracentrifugation, immunoelectrophoresis, and stoichiometry (1:1) of steroid binding. Guinea pig corticosteroid-binding globulin has a molecular weight of 43 300 and contains 29% carbohydrate. The intrinsic fluorescence of the corticosteroid-binding globulin is quenched by about 73% when 1 mol of cortisol is bound. The association constants (pH 7.4) at 4 and 37 degrees C are 2.5 X 10(7) and 1.5 X 10(6) M-1 for cortisol and 1.4 X 10(6) and 0.2 X 10(6) M-1 for progesterone, respectively.

Amino Acids↗
PubMed1978

Steroid-protein interactions. 40. The effect of fatty acids on progesterone binding to human serum albumin.

Human serum albumin was delipidated by solvent extraction or by treatment with charcoal. Progesterone complexes formed with these albumin preparations had higher association constants than those formed with the untreated samples. The charcoal method of delipidation resulted in somewhat higher affinity constants than extraction with chloroform/methanol. Addition of 5 mol lauric acid per mol albumin reduced the association constant of the progesterone complex by approx. 50%. Studies with lauric, myristic, and palmitic acid showed that the decrease of binding affinity for progesterone was proportional to the amount of fatty acid added to albumin, and to its chain length. These results confirm and extend our previous findings of inhibition of progesterone binding to human albumin by long-chain fatty acids.

Binding Sites↗
PubMed1978

Alterations in the ultraviolet absorption spectra of steroids upon binding to serum proteins.

Difference spectra of progesterone-binding globulin (PBG) complexes with progesterone and testosterone were measured. The contributions of steroid and protein to the difference spectra were resolved by use of 5alpha-pregane-3,20-dione and dihydrotestosterone to compensate for the perturbation of PBG. The absorption spectra of seven bound steroids all showed increased extinction coefficients, sharpened absorption bands, a small blue shift, and an increased area implying an enhanced transition moment. This is in contrast to the steroid complexes with the low affinity binders, human serum albumin, and alpha 1-acid glycoprotein, which exhibit decreased extinction coefficients and reduced transition moments.

Alpha-Globulins↗
PubMed1978

Kinetic and equilibrium studies on steroid interaction with human corticosteroid-binding globulin.

Kinetic and equilibrium studies on the interaction of steroids with human corticosteroid-binding globulin (CBG, transcortin) were performed with pH, temperature, and steroid structure as variables. Dissociation rate constants were determined fluorometrically; the values for cortisol, corticosterone, deoxycorticosterone, and progesterone are 0.031, 0.047, 0.10, and 0.16 s-1, respectively, at 20 degrees C, pH 7.4. The pH dependence of the dissociation rate constant for the corticosterone complex below pH 10.5 at 20 degrees C is given by koff = 0.043 (1 + [H+]/10(-6.50)) s-1; above pH 11, koff = 0.030 (1 + 10(-12.15/[H+] s-1. A temperature-dependence study of koff for the cortisol and progesterone complexes gave values of 0.0028 s-1 and 0.012 s-1 at 4 degrees C, respectively, and 0.88 s-1 and 4.5 s-1 at 37 degrees C, with progesterone dissociating about four to five times faster over the entire temperature range. The affinity constants, determined by equilibrium dialysis, for the binding of cortisol, corticosterone, and progesterone at 4 degrees C were 7.9, 7.2, and 7.0 X 10(8) M-1; values of 0.40 and 0.26 X 10(8) M-1 were determined at 37 degrees C for cortisol and progesterone. The close similarity of the affinity constants of the three steroids combined with differing dissociation rates implies that the association rate changes with steroid structure, in contrast to our earlier findings with progesterone-binding globulin.

Adrenal Cortex Hormones↗