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At least 1,153 records · Page 64Linked to original sources
PubMed2001

Inhibition of class C beta-lactamases: structure of a reaction intermediate with a cephem sulfone.

The crystallographic structure of the Enterobacter cloacae GC1 extended-spectrum class C beta-lactamase, inhibited by a new 7-alkylidenecephalosporin sulfone, has been determined by X-ray diffraction at 100 K to a resolution of 1.6 A. The crystal structure was solved by molecular replacement using the unliganded structure [Crichlow et al. (1999) Biochemistry 38, 10256-10261] and refined to a crystallographic R-factor equal to 0.183 (R(free) 0.208). Cryoquenching of the reaction of the sulfone with the enzyme produced an intermediate that is covalently bound via Ser64. After acylation of the beta-lactam ring, the dihydrothiazine dioxide ring opened with departure of the sulfinate. Nucleophilic attack of a side chain pyridine nitrogen atom on the C6 atom of the resultant imine yielded a bicyclic aromatic system which helps to stabilize the acyl enzyme to hydrolysis. A structural assist to this resonance stabilization is the positioning of the anionic sulfinate group between the probable catalytic base (Tyr150) and the acyl ester bond so as to block the approach of a potentially deacylating water molecule. Comparison of the liganded and unliganded protein structures showed that a major movement (up to 7 A) and refolding of part of the Omega-loop (215-224) accompanies the binding of the inhibitor. This conformational flexibility in the Omega-loop may form the basis of an extended-spectrum activity of class C beta-lactamases against modern cephalosporins.

Cephalosporins↗
PubMed2001

Binding and oxidation of alkyl 4-nitrophenyl ethers by rabbit cytochrome P450 1A2: evidence for two binding sites.

Although most cytochrome P450 (P450) reactions demonstrate saturation kinetics that fit to the standard Michaelis-Menten equation, there are important exceptions where sigmoidal or nonhyperbolic behavior is observed and have been fit instead to kinetic models involving two binding sites. To assess these models, we demonstrate the consistency of a two binding site model to interpret both steady-state kinetics and binding events. Rates of 4-nitrophenol and formaldehyde production from the O-demethylation of 1-methoxy-4-nitrobenzene by P450 1A2 isolated from rabbit liver produced biphasic plots, when plotted against substrate concentration. Experiments confirmed the absence of the further oxidation of the products. Recombinant rabbit P450 1A2 yielded the same maximal velocity and more marked biphasicity. Overall, these steady-state data fit well to kinetic models involving two binding sites. Steady-state studies of substrates with bulkier O-ethyl or O-isopropoxy groups indicated decreased affinity for the second site. Based on binding studies, the affinity of P450 1A2 for these substrates increased 200-fold with the larger alkyl groups. To analyze the single binding site model, competition studies were conducted with 1,4-phenyldiisocyanide and the alkyl 4-nitrophenyl ethers. Although the observed dissociation constants and the competing titrant demonstrated a linear dependence, the affinity for the competing titrant depended on the presence of the other titrant, which violates the single binding site model. Alternatively, we applied a two binding site model to these data to obtain dissociation constants for the binary and ternary complexes. The agreement between the dissociation constants for the heterogeneous complexes supports the appropriateness of the two binding site model. This novel finding for P450 1A2 may be more common than originally perceived for P450s.

Animals↗
PubMed2002

Vinylphosphonate internucleotide linkages inhibit the activity of PcrA DNA helicase.

During the past 5 years a great deal of structural and biochemical information has given us a detailed insight into the molecular mechanism of action of the PcrA DNA helicase and challenged previous notions about the molecular mechanism of action of helicases in general. Despite this wealth of information the mechanisms of the interaction of helicases with their DNA substrates and their unidirectional translocation along ssDNA are poorly understood. In this study, we synthesized a chemically modified DNA substrate with reduced backbone rotational flexibility and minimal steric hindrance and studied its effect on the activity of the monomeric 3'-5' DNA helicase, PcrA. Our results show that a single modification on the backbone of the translocating strand is sufficient to inhibit the activity of PcrA helicase, suggesting that rotational flexibility of the backbone is important for efficient unwinding.

Adenosine Triphosphatases↗
PubMed2003

Effects of vinylphosphonate internucleotide linkages on the cleavage specificity of exonuclease III and on the activity of DNA polymerase I.

We have previously reported the synthesis of vinylphosphonate-linked thymidine dimers and their incorporation into synthetic oligonucleotides to create vinylphosphonate internucleotide linkages in the DNA. Such linkages have a profound effect on DNA backbone rotational flexibility, and we have shown that the PcrA helicase, which requires such flexibility, is inhibited when it encounters these linkages on the translocating strand. In this study, we have investigated the effects of these linkages on the dsDNA specific exonuclease III and on the ssDNA specific mung bean nuclease to establish whether our modification confers resistance to nucleases making it suitable for antisense therapy applications. We also investigated the effect on DNA polymerase I to establish whether we could in the future use this enzyme to incorporate these linkages in the DNA. Our results show that a single modification does not affect the activity of DNA polymerase I, but four vinylphosphonate linkages in tandem inhibit its activity. Furthermore, such linkages do not confer significant nuclease resistance to either exonuclease III or mung bean nuclease, but unexpectedly, they alter the cleavage specificity of exonuclease III.

Base Sequence↗
PubMed2004

Functional evaluation of heme vinyl groups in myoglobin with symmetric protoheme isomers.

We replaced protoheme-IX in native myoglobin with the symmetric protohemes-III and -XIII, in order to investigate the role of heme vinyl-globin contacts on Mb function. The UV-visible spectra and the resonance Raman spectra in the high-frequency region (containing oxidation, spin, and coordination state marker lines) of the two reconstituted Mbs were very similar. However, the signal intensity of the Soret band in the CD spectra and the resonance Raman lines for vinyl bending modes in the low-frequency region notably differed, thereby reflecting altered heme peripheral contacts. The redox potentials, formal heterogeneous electron-transfer rates, and thermal denaturation temperatures of the two reconstituted Mbs were also indistinguishable. In addition, the oxygen binding properties of the ferrous deoxy Mbs were comparable. These results demonstrate that altered heme vinyl-globin interactions only slightly affect the physical properties of Mb. It is therefore likely that the orientation of protoheme-IX about the alpha,gamma-axis in the heme pocket is not necessarily a crucial factor for oxygen binding to native Mb.

Animals↗
PubMed2000

Enzymatic synthesis of polyesters from lactones, dicarboxylic acid divinyl esters, and glycols through combination of ring-opening polymerization and polycondensation.

Enzymatic copolymerization of lactones, divinyl esters, and glycols has been performed using lipase as catalyst to produce ester copolymers. The monomers used in this study were 12-, 13-, and 16-membered lactones, divinyl esters of adipic and sebasic acids, and alpha,omega-glycols. Candida antarctica and Pseudomonas cepacia lipases showed relatively high catalytic activity for the present copolymerization, yielding the copolymer having relatively high molecular weight in moderate yields. From 13C NMR analysis, the resulting product was not a mixture of homopolymers, but a copolymer derived from the monomers. NMR data and reaction monitoring results indicate that two different modes of polymerization, ring-opening polymerization and polycondensation, simultaneously take place through enzyme catalysis in one-pot to produce ester copolymers.

Catalysis↗
PubMedDate not supplied

Poly(styrene/alpha-tert-butoxy-omega-vinylbenzylpolyglycidol) microspheres for immunodiagnostics. Principle of a novel latex test based on combined electrophoretic mobility and particle aggregation measurements.

The principle of a novel latex agglutination test based on combined results of electrophoretic mobility and particle aggregation measurements is described. Poly(styrene/alpha-tert-butoxy-omega-vinylbenzylpolyglycidol) (P(S/PGL)) microspheres were synthesized by a one step soap-free emulsion copolymerization of styrene and alpha-tert-butoxy-omega-vinylbenzylpolyglycidol macromonomer with number average molecular weight Mn = 2700 (polydispersity [Mw]/[Mn] = 1.10). Particles with monomodal size distribution (number average diameter Dn = 220 nm) and surface fraction of polyglycidol equal to f = 0.42 mol % were obtained. Human serum albumin (HSA) was covalently bound onto the surface of P(S/PGL) microspheres activated with 1,3,5-trichlorotriazine. In a model immunodiagnostic assay for anti-HSA, in which P(S/PGL) particles with covalently bound HSA have been used, the electrophoretic mobility and aggregation of microspheres were measured simultaneously. This approach allowed detection of anti-HSA in the serum in the range of anti-HSA concentrations from 0.1 to 150 microg/mL. The highest changes in electrophoretic mobility were registered for microspheres with surface concentration of immobilized HSA equal to Gamma = 9.2 x 10(-4) g/m2.

Adsorption↗
PubMedDate not supplied

Novel conjugated linseed oil-styrene-divinylbenzene copolymers prepared by thermal polymerization. 1. Effect of monomer concentration on the structure and properties.

A variety of novel opaque, white polymers ranging from rubbery materials to tough and rigid plastics have been prepared by the thermal polymerization at 85-160 degrees C of varying amounts of 87% conjugated linseed oil, styrene, and divinylbenzene. Gelation of the reactants typically occurs at temperatures higher than 120 degrees C, and fully cured thermosets are obtained after postcuring at 160 degrees C. The fully cured thermosets have been determined by Soxhlet extraction to contain approximately 35-85% cross-linked materials. The microcomposition of these polymers, as determined by 1H NMR spectroscopy, indicates that the cross-linked materials are composed of both soft oily and hard aromatic phases. After solvent extraction, the insoluble materials exhibit nanopores well distributed throughout the polymer matrixes. Dynamic mechanical analysis of these polymers indicates that they are phase separated with a soft rubbery phase having a sharp glass transition temperature of -50 degrees C and a hard brittle plastic phase with a broadened glass transition temperature of 70-120 degrees C. These polymers possess cross-link densities of 0.15-2.41 x 10(4) mol/m3, compressive Young's moduli of 12-438 MPa, and compressive strengths of 2-27 MPa. These materials are thermally stable below 350 degrees C and exhibit a major thermal degradation of 72-90% at 493-500 degrees C.

Fatty Acids, Unsaturated↗
PubMedDate not supplied

Hepatocyte adhesion on a poly[N-p-vinylbenzyl-4-O-beta-D-galactopyranosyl-D-glucoamide]-coated poly(L-lactic acid) surface.

A surface of poly(l-lactic acid) (PLLA) was modified by coating with poly[N-p-vinylbenzyl-4-O-beta-d-galactopyranosyl-d-glucoamide] (PVLA), which was employed to improve the hepatocyte adhesion owing to its amphiphilic property and the presence of a hepatocyte recognition motif. We characterized the surface properties through water contact angle, electron spectroscopy for chemical analysis (ESCA), and scanning probe microscopy (SPM). The effect of PVLA coating on the efficiency of hepatocyte adhesion was evaluated by protein assay and optical microscopy. The surface morphology was under the influence of the concentration of PVLA coating solution and it played a critical role in hepatocyte adhesion. It was confirmed that galactose moieties in PVLA, which can bind to the asialoglycoprotein receptor (ASGPR) on hepatocytes, have a more dominant effect on hepatocyte adhesion than enhanced hydrophilicity. We suggest that the PVLA-PLLA system will be a useful method to improve hepatocyte cell seeding and adhesion onto scaffold matrices.

Animals↗
PubMedDate not supplied

Vinyl polymers based on L-histidine residues. Part 1. The thermodynamics of poly(ampholyte)s in the free and in the cross-linked gel form.

Amphiphilic vinyl polymers (in the free and cross-linked forms), carrying carboxyl and imidazole groups, were prepared by a radical polymerization of the purposely synthesized N-acryloyl-L-histidine. The protonation thermodynamic studies (at 25 degrees C in 0.15 M NaCl) showed high polyelectrolyte character of the soluble polymer. Unlike the linear decreasing trend of the basicity constant, over the whole range of alpha (degree of protonation), the enthalpy changes for the protonation of the imidazole nitrogen in the polymer showed a decreasing pattern only at alpha > 0.5. This was ascribed to the formation of hydrogen bonds between protonated and free neighboring monomer units. Viscometric data revealed a minimum hydrodynamic volume of the polymer at its isoelectric point (pH 5), whereas at higher or lower pHs, the macromolecule expanded greatly as a consequence of the charged sites formation. This produced a preferential solvation of the protonated imidazole and carboxylate ions, the latter being surrounded by more water molecules in the hydration shell. The peculiar hydration behavior was confirmed in the cross-linked polymer. The hydrogel showed an equilibrium degree of swelling (EDS), strongly dependent on pH, in a similar manner as viscometric data of the soluble polymer. A linear relationship between the reduced viscosity and the EDS was found. The polymer was non toxic against the RAW264 cell line.

Animals↗
PubMed2006

Poly(N-vinylformamide)-A drag-reducing polymer for biomedical applications.

Water-soluble drag-reducing polymers (DRPs) were previously demonstrated to significantly increase blood flow, tissue perfusion, and tissue oxygenation when injected intravenously at nanomolar concentrations in various animal models. Turbulent flow drag-reducing ability was proven to be the most important factor defining the potential of polymers to favorably affect blood circulation. Several DRPs were applied in previous in vivo tests, but the search continues for suitable DRPs for biomedical applications. We demonstrated that poly(N-vinylformamide) (PNVF) with a molecular weight of 4.5 x 10(6) Da significantly reduced resistance to turbulent flow in a pipe and thus presents a DRP. We also found that the PNVF mechanical degradation is much slower than that of the most commonly used DRP, poly(ethylene oxide). PNVF is known to have low toxicity. Furthermore, our pilot in vivo study showed that PNVF had acceptable biocompatibility and hemodynamic effectiveness and thus could be considered as a DRP candidate for potential clinical use.

Amides↗
PubMed2000

A facile synthetic approach to L- and P-selectin blockers via copolymerization of vinyl monomers constructing the key carbohydrate modules of sialyl LewisX mimics.

A highly practical synthetic approach is described for artificial L- and P-selectin blockers. The synthesis involves radical bi- and terpolymerizations of p-(N-acrylamido)phenyl 3- or/and 6-sulfo-beta-D-galactoside with allyl alpha-L-fucoside in the presence of acrylamide. Each of the two glycosyl monomers constructs a key carbohydrate module responsible for selectins/sulfated sialyl LewisX (sLeX) bindings. Whereas an acrylamide copolymer carrying 3-sulfo-galactoside showed no activity for any selectins, the fucosylated terpolymer showed a potent activity to block both of P- and L-selectins/sLeX binding at a concentration of a few micrograms per milliliter. The enhanced activity is apparently ascribed to the cooperative binding effects of the fucoside and the 3-sulfo-galactoside residues.

Carbohydrate Sequence↗
PubMedDate not supplied

Spin labeling and kinetic studies of a membrane-immobilized proteolytic enzyme.

Membrane-based bioreactors can greatly influence the rate and extent of chemical reactions and consequently lower the costs associated with the corresponding engineering processes. However, in order to progress in this area, greater understanding of the relationship of the structure and function of bioreactor systems is required. In this study, a proteolytic enzyme, papain (EC 3.4.22.2), was covalently coupled onto the surface of a vinyl alcohol/vinyl butyral copolymer (PVB) membrane employing either glutaraldehyde (GA) or 1,1'-carbonyldiimidazole (CDI). Various kinetic and performance properties of the immobilized papain were studied. It was found that these characteristics of the membrane-bound papain depended on the immobilization method. The CDI-immobilized papain bioreactor was used, although the apparent Michaelis constant, Km, of the CDI-immobilized papain was larger than that of the GA-immobilized enzyme. In separate experiments, a six-carbon spacer was also used between the membrane support and the covalently-linked enzyme. It was found that the insertion of the spacer reduced the disturbance of the enzyme system, resulting in a decreased Km, which was now closer to the value for the free enzyme. Electron paramagnetic resonance (EPR) techniques of spin labeling were used for the first time to examine the conformational change and the active site structure of an enzyme covalently immobilized to a membrane. The structural changes of the active site of papain upon immobilization with and without a spacer were in agreement with the functional properties of the enzyme.

Binding Sites↗
PubMedDate not supplied

Well-defined azlactone-functionalized (co)polymers on a solid support: synthesis via supported living radical polymerization and application as nucleophile scavengers.

Wang resin has been converted to a supported initiator for transition metal-mediated living radical polymerization often called atom-transfer radical polymerization (ATRP) of 2-vinyl-4,4-dimethyl-5-oxazolone (VDM) and styrene (S). Several "Rasta" resins with well-defined macromolecular architectures, including homopolymers PVDM, PS, statistical P(S-stat-VDM), block P(S-b-VDM), and P[S-b-(S-stat-VDM)] copolymers, have been elaborated. For the homopolymerization of VDM and S, a sacrificial initiator, benzyl 2-bromoisobutyrate (BBI), has been introduced to monitor the evolution of molar masses and polydispersity indexes (PDIs) of PS and PVDM onto the Wang resin support without cleavage. After 6 h, 86.7% conversion of VDM is reached, with the isolated PVDM chains having a molar mass of 18 000 g mol(-1) and a PDI value of 1.22. Block copolymers have been synthesized in two steps, involving the synthesis of the PS block isolated at low conversions (<15%) to maintain the bromine end-chain functionality and the subsequent synthesis of the second PVDM or P(S-stat-VDM) block. Polydispersity indexes of the cleaved (co)polymers were low (PDI = 1.11-1.44), and high azlactone loadings have been reached (loading = 6.0 mmol g(-1)). Such azlactone-functionalized Wang resins have shown high efficiency during the scavenging process of benzylamine as monitored by HPLC. Moreover, grafted statistical copolymers have shown the best behavior for removing benzylamine because of an improvement of the accessibility of azlactone rings by the dilution with styrene units.

Free Radical Scavengers↗
PubMed2003

Vinyl bromide as a surrogate for determining vinyl chloride reductive dechlorination potential.

Site evaluation for bioremediation of chlorinated ethenes may need treatability studies to assess the reductive dechlorination potential of vinyl chloride (VC). Dehalogenation of vinyl bromide (VB) was investigated as a surrogate measurement for the dechlorination potential of VC. VB dehalogenation rates and kinetics were studied and compared with those of VC by a methanogenic reductive dechlorinating enrichment culture that was dominated by Dehalococcoides species and by microcosms from two chloroethene-contaminated sites. The enrichment culture dehalogenated VB to ethene at higher rates than VC at similar concentrations. VB was dehalogenated with a higher enzyme affinity than was VC, as indicated by their half-velocity constants, 240 +/- 150 and 21 +/- 8 microM, for VC and VB, respectively. Cross-inhibition study exhibited some evidence for competitive inhibition between VC and VB, suggesting that their degradation might be catalyzed by the same enzyme in the culture. Laboratory microcosm studies using subsurface soil and groundwater from two contaminated sites demonstrated that the production of the reductive dehalogenation product (ethene) could be detected faster with VB as a substrate than with VC. As a result, a substantially shorter (up to 5-10 times) incubation time would be required to detect the same level of reductive dehalogenation activity using VB as a surrogate for VC in treatability assessments.

Bacteria↗
PubMed2006

Product study of the OH, NO3, and O3 initiated atmospheric photooxidation of propyl vinyl ether.

A product study is reported on the gas-phase reactions of OH and NO3 radicals and ozone with propyl vinyl ether (PVE). The experiments were performed in a 405 L borosilicate glass chamber in synthetic air at 298 +/- 3 K using long path in situ FTIR spectroscopy for the analysis of the reactants and products. In the presence of NO(x) (NO + NO2) the main products for the OH-radical initiated oxidation of PVE were propylformate and formaldehyde with molar formation yields of 78.6 +/- 8.8% and 75.9 +/- 8.4%, respectively. In the absence of NO(x) propylformate and formaldehyde were formed with molar formation yields of 63.0 +/- 9.0% and 61.3 +/- 6.3%, respectively. In the reaction of NO3 radicals with PVE propylformate 52.7 +/- 5.9% and formaldehyde 55.0 +/- 6.3% were again observed as major products. The ozonolysis of PVE led to the production of propylformate, formaldehyde, hydroxyperoxymethyl formate (HPMF; HC(O)OCH2OOH), and CO with molar formation yields of 89.0 +/- 11.4%, 12.9 +/- 4.0%, 13.0 +/- 3.4%, and 10.9 +/- 2.6%, respectively. The formation yield of OH radicals in the ozonolysis of PVE was estimated to be 17 +/- 9%. Simple atmospheric degradation mechanisms are postulated to explain the formation of the observed products.

Atmosphere↗