Peptide hairpin nucleation with the obligatory Type I' beta-turn Aib-(D)Pro segment

The alpha-aminoisobutyric acid-D-proline (Aib-(D)Pro) dipeptide is an obligatory Type I' beta-turn forming segment that nucleates hairpin formation.

Relative ability of ovine follicle stimulating hormone and its beta-subunit to generate antibodies having bioneutralization potential in nonhuman primates

The relative ability of ovine follicle stimulating hormone and its beta-subunit, two potential candidates for male contraceptive vaccine, to generate antibodies in monkeys capable of bioneutralizing follicle stimulating hormone was assessed using in vitro model systems. Antiserum against native ovine follicle stimulating hormone was found to be highly specific to the intact form with no cross-reactivity with either of the two subunits while the antiserum against beta-subunit of follicle stimulating hormone could bind to the beta-subunit in its free form as well as when it is combined with alpha-subunit to form the intact hormone. Both antisera could block the binding of the hormone to the receptor if the hormone was preincubated with the antibody. However, the follicle stimulating hormone beta-antisera could only inhibit the binding of the hormone partially (33 percent inhibition) if the antibody and receptor were mixed prior to the addition of the hormone, while antisera to the native follicle stimulating hormone could block the binding completely (100 percent inhibition) in the same experiment. Similarly antisera to the native follicle stimulating hormone was significantly effective in blocking (100 percent) response to follicle stimulating hormone but not the beta-subunit antisera (0 percent) as checked using an in vitro granulosa cell system. Thus the probability of obtaining antibodies of greater bioneutralization potential is much higher if intact hormone is used as an antigen rather than its beta-subunit as a vaccine.

Ability of human chorionic gonadotropin beta-subunit to inhibit the steroidogenic response to lutropin

Ability of the beta-subunit of human chorionic gonadotropin to inhibit the response to lutropin (luteinizing hormone, LH) was tested in the immature rat ovarian system and pregnant-mare-serum-gonadotropin-primed rat ovarian system with progesterone production being used as the response. Human chorionic gonadotropin beta-subunit was found to inhibit human and ovine lutropin-stimulated progesterone production. At a constant dose of lutropin, inhibition was dependent on the concentration of beta-subunit. When concentration of the beta-subunit was kept constant at 5.0 microgram/ml and the concentration of lutropin was varied, the inhibition was maximum at the saturating concentration of the native hormone. The alpha-subunit of the human chorionic gonadotropin did not inhibit the response to lutropin. The lutropin/beta-subunit ratio required to produce an inhibition of response was much lower than that required to bring about an observable inhibition of binding.

Thermodynamic Stability of Potassium-beta-Alumina

The activity of K sub 2 O in a mixture of alpha -alumina and potassium beta -alumina has been determined using a solid state galvanic cell in the temperature range 600-1000K. The cell is written such that the right hand electrode is positive. The solid electrolyte consisted of a dispersion of alpha -alumina ( approx 15 vol.%) in a matrix of K beta -alumina. The emf of the cell was found to be reversible and to vary linearly with temperature. From the emf and auxiliary data on In sub 2 O sub 3 and K sub 2 O from the literature, the activity of K sub 2 O in the two-phase mixture is obtained. The standard free energy of formation of K beta -alumina from component oxides is given. Graphs.

Criticality of the exponential rate of decay for the largest nearest-neighbor link in random geometric graphs

Let n points be placed independently in d-dimensional space according to the density f(x) = A(d)e(-lambda parallel to x parallel to alpha), lambda, alpha > 0, x is an element of R-d, d >= 2. Let d(n) be the longest edge length of the nearest-neighbor graph on these points. We show that (lambda(-1) log n)(1-1/alpha) d(n) - b(n) converges weakly to the Gumbel distribution, where b(n) similar to ((d - 1)/lambda alpha) log log n. We also prove the following strong law for the normalized nearest-neighbor distance (d) over tilde (n) = (lambda(-1) log n)(1-1/alpha) d(n)/log log n: (d - 1)/alpha lambda <= lim inf(n ->infinity) (d) over tilde (n) <= lim sup(n ->infinity) (d) over tilde (n) <= d/alpha lambda almost surely. Thus, the exponential rate of decay alpha = 1 is critical, in the sense that, for alpha > 1, d(n) -> 0, whereas, for alpha <= 1, d(n) -> infinity almost surely as n -> infinity.

Conformational properties of hybrid peptides containing alpha and omega-amino acids

This review briefly surveys the conformational properties of guest omega-amino acid residues when incorporated into host alpha-peptide sequences. The results presented focus primarily on the use of beta- and gamma-residues in alphaomega sequences. The insertion of additional methylene groups into peptide backbones enhances the range of accessible conformations, introducing additional torsional variables. A nomenclature system, which permits ready comparisons between alpha-peptides and hybrid sequences, is defined. Crystal structure determination of hybrid peptides, which adopt helical and beta-hairpin conformations permits the characterization of backbone conformational parameters for beta- and gamma-residues inserted into regular alpha-polypeptide structures. Substituted beta- and gamma-residues are more limited in the range of accessible conformation than their unsubstituted counterparts. The achiral beta,beta-disubstituted gamma-amino acid, gabapentin, is an example of a stereochemically constrained residue in which the torsion angles about the C-beta-C-gamma (theta(1)) and C-alpha-C-beta (theta(2)) bonds are restricted to the gauche conformation. Hybrid sequences permit the design of novel hydrogen bonded rings in peptide structures.

Ability of human chorionic gonadotropin beta-subunit to inhibit the steroidogenic response to lutropin.

Ability of the beta-subunit of human chorionic gonadotropin to inhibit the response to lutropin (luteinizing hormone, LH) was tested in the immature rat ovarian system and pregnant-mare-serum-gonadotropin-primed rat ovarian system with progesterone production being used as the response. Human chorionic gonadotropin beta-subunit was found to inhibit human and ovine lutropin-stimulated progesterone production. At a constant dose of lutropin, inhibition was dependent on the concentration of beta-subunit. When concentration of the beta-subunit was kept constant at 5.0 microgram/ml and the concentration of lutropin was varied, the inhibition was maximum at the saturating concentration of the native hormone. The alpha-subunit of the human chorionic gonadotropin did not inhibit the response to lutropin. The lutropin/beta-subunit ratio required to produce an inhibition of response was much lower than that required to bring about an observable inhibition of binding.

Biochemical and structural characterization of recombinant hyoscyamine 6 beta-hydroxylase from Datura metel L.

Hyoscyamine 6 beta-hydroxylase (H6H; EC 1.14.11.11), an important enzyme in the biosynthesis of tropane alkaloids, catalyzes the hydroxylation of hyoscyamine to give 6 beta-hydroxyhyoscyamine and its epoxidation in the biosynthetic pathway leading to scopolamine. Datura metel produces scopolamine as the predominant tropane alkaloid. The cDNA encoding H6H from D. mete! (DmH6H) was cloned, heterologously expressed and biochemically characterized. The purified recombinant His-tagged H6H from D. mete! (DmrH6H) was capable of converting hyoscyamine to scopolamine. The functionally expressed DmrH6H was confirmed by HPLC and ESI-MS verification of the products, 6 beta-hydroxyhyoscyamine and its derivative, scopolamine; the DmrH6H epoxidase activity was low compared to the hydroxylase activity. The K-m values for both the substrates, hyoscyamine and 2-oxoglutarate, were 50 mu M each. The CD (circular dichroism) spectrum of the DmrH6H indicated a preponderance of alpha-helicity in the secondary structure. From the fluorescence studies, Stern-Volmer constants for hyoscyamine and 2-oxoglutarate were found to be 0.14 M-1 and 0.56 M-1, respectively. These data suggested that the binding of the substrates, hyoscyamine and 2-oxoglutarate, to the enzyme induced significant conformational changes. (C) 2010 Elsevier Masson SAS. All rights reserved.

Conformational Studies of Some Alpha-substituted Acetones CH3COCH2XCH3 Where X=CH2, O Or S And Phenacyl Sulfide

Both semiempirical and ab initio calculations are reported for conformational studies of a series of alpha-substituted acetones CH3COCH2XCH3 where X = CH2, O or S and of phenacyl sulfide PhCOCH2SCH3. For conformational studies in the lowest triplet state of these molecules, the MINDO/3 method was employed in the unrestricted Hartree-Fock frame. Results reveal that rotation around a bond alpha to the carbonyl group is more favourable than that around the beta bond. The preferred conformations in the lowest triplet state are nearly the same as in the ground state.

Effect of tolerance on the propagation characteristic of a superconducting thin film microstrip delay line

The propagation constant of a superconducting microstrip transmission delay line is evaluated using the spectral domain immitance approach, modelling the superconductor as a surface current having an equivalent surface impedance found through the complex resistive boundary condition. The sensitivity approach is used to study the beta variations with substrate parameters and film characteristics. Results show that the surface impedance does not have much influence on beta sensitivities with respect to epsilon r, W and h. However, it can be observed that the surface impedance plays a crucial role in determining the optimum design.

Microwave Irradiation Assisted Method for the Rapid Synthesis of fine Particles of alpha Al2O3 And alpha (Al1-XCrx)(2)O-3 And Their Coatings on Si(100)

Chromium substituted beta diketonate complexes of aluminium have been synthesized and employed as precursors for a novel soft chemistry process wherein microwave irradiation of a solution of the complex yields within minutes well crystallized needles of alpha (Al1 XCrx)(2)O-3 measuring 20 30 nm in diameter and 50 nm long By varying the microwave irradiation parameters and using a surfactant such as polyvinyl pyrrolidone the crystallite size and shape can be controlled and their agglomeration prevented These microstructural parameters as well as the polymorph of the Cr substituted Al2O3 formed may also be controlled by employing a different complex Samples of alpha (Al1 XCrx)(2)O-3 have been characterized by XRD FTIR and TEM The technique results in material of homogeneous metal composition, as shown by EDAX and can be adjusted as desired The technique has been extended to obtain coatings of alpha (Al1 XCrx)(2)O-3 on Si(100)

Structure of N-tert-butyloxycarbonyl-[alpha]-aminoisobutyryl-DL-pipecolyl-[alpha]-aminoisobutyric acid methyl ester

C20H35N3O6 (Boc-Aib-DL-Pip-Aib-OMe, Boc = tert-butyloxycarbonyl, Aib = alpha-aminoisobutyric acid, Pip = pipecolic acid, OMe = methoxy), M(r) = 413.5, monoclinic, P2(1)/c, a = 18.055 (3), b = 15.048 (3), c = 17.173 (3) angstrom, beta = 91.7 (1)-degrees, V = 4663.8 (9) angstrom3, Z = 8, D(m) = 1.16, D(x) = 1.178 Mg m-3, lambda(Mo Kalpha) = 0.71069 angstrom, mu = 0.081 mm-1, F(000) = 1792, T = 297 K. The final R value for 4925 [I greater-than-or-equal-to 3sigma(I)] reflections is 0.065 (wR = 0.067). The peptide backbone of the two independent molecules in the asymmetric unit is folded at the -Aib-Pip- sequence to form a type-I (I') beta-bend stabilized by a 1 <-- 4 intramolecular N-H...O=C hydrogen bond between the Aib(3) peptide N-H and Boc urethane C=O groups.

Influence of glycosidic linkage on the nature of carbohydrate binding in beta-prism I fold lectins: An X-ray and molecular dynamics investigation on banana lectin-carbohydrate complexes

The three crystal structures reported here provide details of the interactions of mannose and the mannosyl-alpha-1,3-mannose component of a pentamannose with banana lectin and evidence for the binding of glucosyl-alpha-1,2-glucose to the lectin. The known structures involving the lectin include a complex with glucosyl-beta-1,3-glucose. Modeling studies on the three disaccharide complexes with the reducing end and the nonreducing end at the primary binding site are also provided here. The results of the Xray and modeling studies show that the disaccharides with an alpha-1,3 linkage prefer to have the nonreducing end at the primary binding site, whereas the reducing end is preferred at the site when the linkage is beta-1,3 in mannose/glucose-specific beta-prism I fold lectins. In the corresponding galactose-specific lectins, however, alpha-1,3-linked disaccharides cannot bind the lectin with the nonreducing end at the primary binding site on account of steric clashes with an aromatic residue that occurs only when the lectin is galactose-specific. Molecular dynamics simulations based on the known structures involving banana lectin enrich the information on lectin-carbohydrate interactions obtained from crystal structures. They demonstrate that conformational selection as well as induced fit operate when carbohydrates bind to banana lectin.

Collective Effects on Single Particle Orientational Relaxation in Slow Dipolar Liquids

Theoretical and computer simulation studies of orientational relaxation in dense molecular liquids are presented. The emphasis of the study is to understand the effects of collective orientational relaxation on the single-particle orientational dynamics. The theoretical analysis is based on a recently developed molecular hydrodynamic theory which allows a self-consistent description of both the collective and the single-particle orientational relaxation. The molecular hydrodynamic theory can be used to derive a relation between the memory function for the collective orientational correlation function and the frequency-dependent dielectric function. A novel feature of the present work is the demonstration that this collective memory function is significantly different from the single-particle rotational friction. However, a microscopic expression for the single-particle rotational friction can be derived from the molecular hydrodynamic theory where the collective memory function can be used to obtain the single-particle orientational friction. This procedure allows, us to calculate the single-particle orientational correlation function near the alpha-beta transition in the supercooled liquid. The calculated correlation function shows an interesting bimodal decay below the bifurcation temperature as the glass transition is approached from above. Brownian dynamics simulations have been carried out to check the validity of the above procedure of translating the memory function from the dielectric relaxation data. We have also investigated the following two issues important in understanding the orientational relaxation in slow liquids. First, we present an analysis of the ''orientational caging'' of translational motion. The value of the translational friction is found to be altered significantly by the orientational caging. Second, we address the question of the rank dependence of the dielectric friction using both simulation and the molecular hydrodynamic theory.

Sintering of beta titanium: Role of dislocation pipe diffusion

Sintering of titanium in its high temperature beta phase was studied by isothermal dilatometry. The sintering shrinkage y did not follow the normal time exponent type of behaviour, instead being described by the equation y = Kt(m)/[1-(A+Bt)(2)], where m = 1.93 +/- 0.07, with an activation energy of 62-90 kJ mol(-1). A detailed analysis of these results, based on the 'anomalous' diffusion behaviour reported for beta titanium, is carried out. It is shown that the generation of a high density of dislocations during the alpha --> beta phase transformation, coupled with sluggish recovery at the sintering necks, enables sintering mass transport by pipe diffusion through dislocation cores from sources of matter within the particles to become dominant.