An NMR study of the interaction of cytosine arabinoside and lysozyme

Abstract is not available.

Partial Loss Of Support And Frame-Soil Interaction

An interaction analysis has been conducted to study the effects of a local loss of support beneath the beam footing of a two-bay plane frame. The results of the study indicate that the magnitude of increase in the bending moment and axial force in the structure due to the presence of a void are dependent, not only on the extent of support loss, but also on the relative stiffnesses between foundation beam and soil, and between superstructure and soil. The increase in bending moment even for a void span of 1/12 of the foundation beam length can become so significant as to exceed the safety provisions. The study shows that the effect of a void on the superstructure moments can be greatly minimized by a combination of rigid foundation and flexible superstructure.

Use of α- and β-subunit specific antibodies in studying interaction of hCG with Leydig cell receptors

Antisera (a/s) raised to individual α- and β-subunits of human chorionic gonadotropin (hCG) have been characterized for specificity using immunoaffinity procedures and used to study the disposition of the two subunits when intact hCG is complexed with luteinizing hormone (LH) receptor of the Leydig cells. Three kinds of experiments were done. (a) The ability of the preformed hormone-antibody (H-Ab) complex to bind to receptor and stimulate a response; (b) the ability of the a/s to dissociate hCG from its complex with the receptor and thereby terminate response; and (c) the ability of the premixed antibody and receptor to compete for binding of labeled hCG. Although the subunit specific a/s used here were equipotent in binding hCG (capacity to bind and Ka being very similar), their behavior once the receptor preparation or Leydig cell is introduced into the system was drastically different. The β-subunit antibody relative to the α-subunit antibody, appeared to be poorly effective in preventing hCG from either binding to the receptor or inhibiting the continuation of response. The results suggest that hCG upon interaction with the receptor loses the determinants specific to the β-region more rapidly compared to those specific to the α-region suggesting thereby that the initial interaction of hCG with the receptor should be occurring through sites in the β-subunit. Although the α-subunit portion of the hCG molecule is available for binding to the antibody for a relatively longer time, the biological response of the cell seems very sensitive to such binding with the antibody as it invariably results in loss of response. In the Leydig cell system, the ability of the a/s to bind hCG that is already complexed to the receptor appears to be dependent upon the time of addition of the antibody to the incubation medium. The antisera were totally ineffective in inhibiting steroidogenic response to hCG if added 60 min after addition of hCG. This would suggest that the hormone-receptor complex once formed perhaps continues to change its orientation with the result that with time relatively less and less of antigenic determinants become available for antibody binding.

Interaction Between Two Residues in the Inter-Domain Interface of Escherichia coli Peptidase N Modulates Catalytic Activity

The role of interaction between Asn259 (catalytic domain) with Gln821 (C-terminal domain) in PeptidaseN was investigated. The k(cat) of PeptidaseN containing Asn259Asp or Gln821Glu is enhanced whereas it is suppressed in Asn259AspGln821Glu. Structural analysis shows this interaction to change the relative disposition of active site residues, which modulates catalytic activity.

Effect of chelating anions on metal-crown interaction. Part III. X-ray structure of potassium picrate complex of benzo-15-crown-5

The cr~¢stal structure of [potassium(benzo-15-crown-5)](picrate) shows that in the complex the metal is sandwiched between two crowns andhas no interaction with plcrate.

X-ray and ultraviolet photoelectron spectroscopy studies of the interaction of carbon monoxide with oxygen adsorbed on silver covered with potassium, caesium or barium

X-ray and He(II) ultraviolet photoelectron spectroscopy studies of the interaction of CO with oxygen on potassium-, caesium- and barium-covered Ag surfaces have shown the formation of carbonate at 300 K. While on a caesium-covered surface only carbonate formation takes place, on the potassium- and barium-covered surfaces molecularly chemisorbed CO is also formed. The variation of the surface concentrations of carbon and oxygen with temperature has been examined and a reaction sequence for the interaction of CO with adsorbed oxygen on potassium-, caesium- and barium-covered Ag surfaces is suggested.

Structural Basis of Drug Resistance by Genetic Variants of HIV Type 1 Clade C Protease from India

Using computer modeling of three-dimensional structures and structural information available on the crystal structures of HIV-1 protease, we investigated the structural effects of mutations, in treatment-naive and treatment-exposed individuals from India and postulated mechanisms of resistance in clade C variants. A large number of models (14) have been generated by computational mutation of the available crystal structures of drug bound proteases. Localized energy minimization was carried out in and around the sites of mutation in order to optimize the geometry of interactions present. Most of the mutations result in structural differences at the flap that favors the semiopen state of the enzyme. Some of the mutations were also found to confer resistance by affecting the geometry of the active site. The E35D mutation affects the flap structure in clade B strains and E35N and E35K mutation, seen in our modeled strains, have a more profound effect. Common polymorphisms at positions 36 and 63 in clade C also affected flap structure. Apart from a few other residues Gln-58, Asn-83, Asn-88, and Gln-92 and their interactions are important for the transition from the closed to the open state. Development of protease inhibitors by structure-based design requires investigation of mechanisms operative for clade C to improve the efficacy of therapy.

Interaction of carbon monoxide with transition metal surfaces

XPS studies of the interaction of carbon monoxide with surfaces of Fe, Co and Ni indicate that at 300 K, the disproportionation reaction is prominent up to exposures of 103 L giving rise to high surface concentrations of carbon. At higher exposures and higher temperatures, dissociation of carbon monoxide accompanied by the formation of surface oxide layers becomes more prominent. In the case of copper, disproportionation is prominent up to 104 L even at 500 K followed by dissociation at higher exposures. These results are also supported by Auger spectroscopic studies.

Constraint effects on multiple void interaction in pressure sensitive plastic solids

In this work, effects of pressure sensitive yielding and plastic dilatancy on void growth and void interaction mechanisms in fracture specimens displaying high and low constraint levels are investigated. To this end, large deformation finite element simulations are carried out with discrete voids ahead of the notch. It is observed that multiple void interaction mechanism which is favored by high initial porosity is further accelerated by pressure sensitive yielding, but is retarded by loss of constraint. The resistance curves predicted based on a simple void coalescence criterion show enhancement in fracture resistance when constraint level is low and when pressure sensitivity is suppressed.

Interaction of Cibacron Blue F3G-A and Procion Red HE-3B with sheep liver 5,10-methylenetetrahydrofolate reductase

Cibacron Blue F3G-A, a probe used to monitor nucleotide binding domains in enzymes, inhibited sheep liver 5, 10-methylenetetrahydrofolate reductase competitively with respect to 5-methyltetrahydrofolate and NADPH. The Ki values obtained by kinetic methods and the Kd value for the binding of the dye to the enzyme estimated by protein fluorescence quenching were in the range 0·9-1·2 μM. Another triazine dye, Procion Red HE-3B interacted with the enzyme in an essentially similar manner to that observed with Cibacron Blue F3G-A. These results as well as the interaction of the dye with the enzyme monitored by difference spectroscopy and intrinsic protein fluorescence quenching methods indicated that the dye was probably interacting at the active site of the enzyme by binding at a hydrophobic region.

Structure and Conformation of an Antidepressant Drug, Nitroxazepine Hydrochloride Monohydrate

CIsH20N3Oa+.C1-.H2 O, M r = 395, orthorhombic, Pn21a, a = 7.710 (4), b = 11.455 (3), c -- 21.199 (3)/k, Z = 4, V = 1872.4/k 3, D m = 1.38, D C = 1.403 g cm -3, F(000) = 832, g(Cu Kct) = 20.94 cm -l. Intensities for 1641 reflections were measured on a Nonius CAD-4 diffractometer; of these, 1470 were significant. The structure was solved by direct methods and refined to an R index of 0.045 using a blockdiagonal least-squares procedure. The angle between the least-squares planes through the benzene rings is 125.0 (5) ° and the side chain is folded similarly to one of the independent molecules of imipramine hydrochloride.

Kinetics of interaction of Cotton Leaf Curl Kokhran Virus-Dabawali (CLCuKV-Dab) coat protein and its mutants with ssDNA

Gemini viral assembly and transport of viral DNA into nucleus for replication, ssentially involve DNA-coat protein interactions. The kinetics of interaction of Cotton LeafCtirl Kokhran Virus-Dabawali recombinant coat protein (rCP) with DNA was studied by electrophoretic mobility shift assay (EMSA) and Surface plasmon resonance (SPR). The rCP interacted with ssDNA with a K-A, of 2.6 +/- 0.29 x 10(8) M-1 in a sequence non-specific manner. The CP has a conserved C2H2 type zinc finger motif composed of residues C68, C72, H81 and H85. Mutation of these residues to alanine resulted in reduced binding to DNA probes. The H85A mutant rCP showed the least binding with approximately 756 fold loss in the association rate and a three order magnitude decrease in the binding affinity as compared to rCP. The CP-DNA interactions via the zinc finger motif could play a Crucial role ill Virus assembly and in nuclear transport. (C) 2009 Elsevier Inc.

Interaction of manganese(II) with valinomycin: Observation of mixed complexes

The interaction of antibiotic valinomycin with manganese (II) has been studied using circular dichroism, electron spin resonance and infrared techniques. Results show that Mn(II) forms complexes with valinomycin in both 2:1 (valinomycin-ion-valinomycin sandwich) and 1:1 (equimolar) stoichiometries. The 1:1 type observed here is very different from the well known K+-valinomycin bracelet conformation.

Coordinative interaction of morpholine with divalent metallo tetraphenyl porphyrins

The formation of axially coordinated morpholine (morph) complexes of MTPP, (M = Co, Ni, Cu and Zn) has been studied. Morpholine coordinates through imino nitrogen to the metal ions with the retainment of equatorial conformation. The presence of spin-free, NiTPP (morph), (S = 1) and an equilibrium mixture of CoTPP and an oxygen adduct of CoTPP (morph) in solution have been observed.

Resolution of racemic gossypol and interaction of individual enantiomers with serum albumins and model peptides

Racemic gossypol has been resolved by HPLC separation of diastereomeric (−) norepinephrine adducts on a reverse-phase column. The binding constants for the interaction of the three gossypol forms (+, − and −) with human and bovine serum albumins have been determined by fluoresence quenching studies. The KD values demonstrate that all three forms bind equally effectively to the two proteins, suggesting an absence of chiral discrimination in albumin-gossypol interactions. Circular dichroism studies of (+)-gossypol binding to the model dibasic peptides, Boc-Lys-Pro-Aib-Lys-NHMe and gramicidin S, suggesting that distortions of binaphthyl geometry may occur only for specific orientations of interacting residues at the receptor site.