Rabbit CYP4B1 engineered for high-level expression in Escherichia coli: ligand stabilization and processing of the N-terminus and heme prosthetic group

Modifications at the N-terminus of the rabbit CYP4B1 gene resulted in expression levels in Escherichia coli of up to 660 nmol/L. Solubilization of the enzyme from bacterial membranes led to substantial conversion to cytochrome P420 unless alpha-naphthoflavone was added as a stabilizing ligand. Mass spectrometry analysis and Edman sequencing of purified enzyme preparations revealed differential N-terminal post-translational processing of the various constructs expressed. Notably, bacterial expression of CYP4B1 produced a holoenzyme with >98.5% of its heme prosthetic group covalently linked to the protein backbone. The near fully covalently linked hernoproteins exhibited similar rates and regioselectivities of lauric acid hydroxylation to that observed previously for the partially heme processed enzyme expressed in insect cells. These studies shed new light on the consequences of covalent heme processing in CYP4B1 and provide a facile system for future mechanistic and structural studies with the enzyme. (C) 2003 Elsevier Science (USA). All rights reserved.

A novel method to prepare mesoporous nano-zirconia

A novel method to prepare mesoporous zirconia was developed. The synthesis was carried out in the presence of PEO surfactants via solid-state reaction. The materials exhibit strong diffraction peak at low 2-theta angle and their nitrogen adsorption/desorption isotherms are typical of IV type with H3 hysteresis loops. The pore structure examined by TEM can be described as wormhole domains. The tetragonal zirconia nanocrystals are uniform in size (around 1.5nm) and their pores center at around 4.6nm. The zirconia nanocrystal growth is mainly via an aggregation mechanism. This study also reveals that the PEO surfactants can interact with the Zr-O-Zr framework to reinforce the thermal stability of zirconia. The ratio of NaOH to ZrOCl2, crystallization and calcination temperature play an important role in the synthesis of mesoporous zirconia.

Price stabilization and the risk-averse firm

An analytically simple and tractable approach to firm-level welfare analysis of complete and partial mean-preserving price stabilization for producers with general risk-averse preferences facing a stochastic technology is developed. Necessary and sufficient conditions for price stabilization to be welfare enhancing are derived under different assumptions of the producer's preferences and the producer's technology. Existing stabilization results for the risk-averse firm are shown to be corollaries of these more general results.

Rehabilitation of pelvic floor muscles utilizing trunk stabilization

The pelvic floor muscles (PFM) are part of the trunk stability mechanism. Their function is interdependent with other muscles of this system. They also contribute to continence, elimination, sexual arousal and intra-abdominal pressure. This paper outlines some aspects of function and dysfunction of the PFM complex and describes the contribution of other trunk muscles to these processes. Muscle pathophysiology of stress urinary incontinence (SUI) is described in detail. The innovative rehabilitation programme for SUI presented here utilizes abdominal muscle action to initiate tonic PFM activity. Abdominal muscle activity is then used in PFM strengthening, motor relearning for functional expiratory actions and finally impact training. (C) 2003 Elsevier Ltd. All rights reserved.

Microstructure and application of mesoporous nanosize zirconia

The mesoporous nanoscale zircoina zeolite was firstly synthesized via solid state - Structure directing method without addition of any stabilizer. The sample bears lamellar or worm pore structures, relatively high surface area compared with that reported. The mesoporous nanosize structure can also resist higher calcination temperature. The introduction of above zirconia to the catalyst of methanol synthesis dedicates the nanosize particle size to the catalyst, which significantly changes the physical structure and electronic effect of the catalyst. The catalyst shows higher catalytic activity and selectivity to methanol. The active sites for methanol synthesis are demonstrated over various catalysts in this paper.

Postsynthesis stabilization of free-standing mesoporous silica films

Mixed ammonia-water vapor postsynthesis treatment provides a simple and convenient method for stabilizing mesostructured silica films. X-ray diffraction, transmission electron microscopy, nitrogen adsorption/desorption, and solid-state NMR (C-13, Si-29) were applied to study the effects of mixed ammonia-water vapor at 90 degreesC on the mesostructure of the films. An increased cross-linking of the silica network was observed. Subsequent calcination of the silica films was seen to cause a bimodal pore-size distribution, with an accompanying increase in the volume and surface area ratios of the primary (d = 3 nm) to secondary (d = 5-30 nm) pores. Additionally, mixed ammonia-water treatment was observed to cause a narrowing of the primary pore-size distribution. These findings have implications for thin film based applications and devices, such as sensors, membranes, or surfaces for heterogeneous catalysis.

Dynamic interfacial tension of aqueous solutions of PVAAs and its role in liquid-liquid dispersion stabilization

In liquid-liquid dispersion systems, the dynamic change of the interfacial properties between the two immiscible liquids plays an important role in both the emulsification process and emulsion stabilization. In this paper, experimentally measured dynamic interfacial tensions of 1-chlorobutane in the aqueous solutions of various random copolymers of polyvinyl acetate and polyvinyl alcohol (PVAA) are presented. Theoretical analyses on these results suggest that the adsorption of the polymer molecules is controlled neither by the bulk diffusion process nor the activation energy barrier for the adsorption but the conformation of polymer molecules. Based on the concept of critical concentration of condensation for polymer adsorption, as well as the observation that the rate at which the dynamic interfacial tension changes does not correlate to the PVAA's ability to stabilize a single drop, it is postulated that the main stabilization mechanism for the PVAAs is by steric hindrance, not the Gibbs-Marangoni effect offered by the small molecule surfactants.

Engineering stable peptide toxins by means of backbone cyclization: Stabilization of the alpha-conotoxin MII

Conotoxins (CTXs), with their exquisite specificity and potency, have recently created much excitement as drug leads. However, like most peptides, their beneficial activities may potentially be undermined by susceptibility to proteolysis in vivo. By cyclizing the alpha-CTX MII by using a range of linkers, we have engineered peptides that preserve their full activity but have greatly improved resistance to proteolytic degradation. The cyclic MII analogue containing a seven-residue linker joining the N and C termini was as active and selective as the native peptide for native and recombinant neuronal nicotinic acetylcholine receptor subtypes present in bovine chromaffin cells and expressed in Xerl oocytes, respectively. Furthermore, its resistance to proteolysis against a specific protease and in human plasma was significantly improved. More generally, to our knowledge, this report is the first on the cyclization of disulfide-rich toxins. Cyclization strategies represent an approach for stabilizing bioactive peptides while keeping their full potencies and should boost applications of peptide-based drugs in human medicine.

Suppression of spurious intermediate frequency modes in under-integrated elements by combined stiffness/viscous stabilization

Solutions employing perturbation stiffness or viscous hourglass control with one-point quadrature finite elements often exhibit spurious modes in the intermediate frequency range. These spurious frequencies are demonstrated in several examples and their origin is explained. Then it is shown that by critically damping the hourglass modes, these spurious mid-range frequency modes can be suppressed. Estimates of the hourglass frequency and damping coefficients are provided for the plane 4-node quadrilateral and a 4-node shell element. Results are presented that show almost complete annihilation of spurious intermediate frequency modes for both linear and non-linear problems. Copyright (c) 2005 John Wiley & Sons, Ltd.

Nanocrystalline zirconia as catalyst support in methanol synthosis

Nanocrystalline zirconia was synthesized and used as catalyst support for methanol synthesis. The nanocrystallite particles have new physical and textural properties which are critical in determining the catalytic performance. Nanocrystalline zirconia changes the electronic structure and affects the metal and support interactions on the catalyst. leading to facile reduction. intimate interaction between copper and zirconia, more corner defects and oxygen vacancies on the surface of the catalyst. All these changes are beneficial to the reaction of methanol synthesis from hydrogenation of CO2. As a result. higher conversion of CO2 and selectivity of methanol are achieved compared to the catalysts prepared by conventional co-precipitation method. (C) 2004 Elsevier B.V. All rights reserved.

Mesoporous nanocrystalline zirconia with lamellar and MSU structure

Without introduction of any stabilizer, the mesoporous nanocrystalline zirconia with lamellar and MSU structure was obtained via solid state reaction coupled with surfactant templating method. The phase, surface area and pore structure of zirconia prepared with this novel method could be designed, tailored and controlled by varying synthesis parameters. The phase transformation was controlled by particle size. The mesostructure possesses nanocrystalline pore wall, which renders it more thermally stable than amorphous framework. The results suggest strongly that in solid state synthesis system mesostructure formation still follow the supramolecular self-assembly mechanism. The lamellar and reverse hexagonal structure could be transformed at different OH-/Zr molar ratios in order to sustain the low surface energy of the mesophases. The lamellar structure was preferred at higher OH-/Zr molar ratios but reverse hexagonal was at low ratios.

The complexity of p53 stabilization and activation

A number of proteins are activated by stress stimuli but none so spectacularly or with the degree of complexity as the tumour suppressor p53 (human p53 gene or protein). Once stabilized, p53 is responsible for the transcriptional activation of a series of proteins involved in cell cycle control, apoptosis and senescence. This protein is present at low levels in resting cells but after exposure to DNA-damaging agents and other stress stimuli it is stabilized and activated by a series of post-translational modifications that free it from MDM2 (mouse double minute 2 but used interchangeably to denote human also), a ubiquination ligase that ubiquitinates it prior to proteasome degradation. The stability of p53 is also influenced by a series of other interacting proteins. In this review, we discuss the post-translational modifications to p53 in response to different stresses and the consequences of these changes.

Role of nanosized zirconia on the properties of Cu/Ga2O3/ZrO2 catalysts for methanol synthesis

The introduction of mesoporous nanosize zirconia to the catalyst for methanol synthesis dedicates the nanosized catalyst and mesoporous duplicated properties. The catalyst bears the larger surface area, larger mesoporous volume and more uniform diameter, more surface metal atoms and oxygen vacancies than the catalyst prepared with the conventional coprecipitation method. The modification of microstructure and electronic effect could result in the change of the reduced chemical state and decrease of reducuction temperature of copper, donating the higher activity and methanol selectivity to the catalyst. The results of methanol synthesis demonstrate that the Cu+ is the optimum active site. Also, the interaction between the copper and zirconia shows the synergistic effect to fulfil the methanol synthesis.