Solution rheology of kappa-carrageenan in the ordered and disordered conformations

The order-disorder conformational transition of kappa-carrageenan, induced by both electrolyte and temperature, was found to give rise to significantly different rheological properties under shear flow, extensional flow, and small deformation oscillation regimes. Shear flow displayed only shear thinning or Newtonian behavior, depending of the chain conformation. A larger range of properties was observed in elongational flow. Strain-thinning behavior was observed in the ordered conformation while strain thickening occurred in the disordered conformation. These results are discussed as a function of the chain conformation.

Is the internet an integral part of general practice in Australia?

Computerisation has seen significant changes in information management and procedures in General Practice. Whilst the majority of changes to date, have been apparent in administration, the clinical aspect of primary care is now increasingly taking advantage of the computer and significantly, the Internet. The professional obligation to maintain currency in medical developments has provided an opportunity to use the Internet as a low cost method to access a wide range of medical research information worldwide. Furthermore traditional methods of communication within the medical community have the potential to be transformed by the availability and use of electronic communication techniques such as email. The incorporation of these new technologies in clinical practice is not without its challenges, and includes quality, timeliness, information management and attitudes to Internet based information. This paper presents the results of a preliminary study of GP's undertaken in Western Australia analysing the usage of, and attitude to, the Internet in clinical practice.

Crystallographic and biochemical analyses of the metal-free Haemophilus influenzae Fe3+-binding protein

The crystal structure of the iron-free (apo) form of the Haemophilus influenzae Fe(3+)-binding protein (hFbp) has been determined to 1.75 A resolution. Information from this structure complements that derived from the holo structure with respect to the delineation of the process of iron binding and release. A 21 degrees rotation separates the two structural domains when the apo form is compared with the holo conformer, indicating that upon release of iron, the protein undergoes a change in conformation by bending about the central beta-sheet hinge. A surprising finding in the apo-hFbp structure was that the ternary binding site anion, observed in the crystals as phosphate, remained bound. In solution, apo-hFbp bound phosphate with an affinity K(d) of 2.3 x 10(-3) M. The presence of this ternary binding site anion appears to arrange the C-terminal iron-binding residues conducive to complementary binding to Fe(3+), while residues in the N-terminal binding domain must undergo induced fit to accommodate the Fe(3+) ligand. These observations suggest a binding process, the first step of which is the binding of a synergistic anion such as phosphate to the C-terminal domain. Next, iron binds to the preordered half-site on the C-terminal domain. Finally, the presence of iron organizes the N-terminal half-site and closes the interdomain hinge. The use of the synergistic anion and this iron binding process results in an extremely high affinity of the Fe(3+)-binding proteins for Fe(3+) (nFbp K'(eff) = 2.4 x 10(18) M(-1)). This high-affinity ligand binding process is unique among the family of bacterial periplasmic binding proteins and has interesting implications in the mechanism of iron removal from the Fe(3+)-binding proteins during FbpABC-mediated iron transport across the cytoplasmic membrane.

A rheological study of the order-disorder conformational transition of xanthan gum

The rheological properties of a moderately concentrated solution of xanthan gum in both the ordered and the disordered state have been studied. Oscillatory shear, steady shear flow, and extensional flow experiments have been performed at different temperatures, covering the order-disorder transition determined by differential scanning calorimetry (DSC). The principle of time/temperature superposition was applied to the xanthan solutions for the different types of flow. Although a master curve covering six decades of frequency could be obtained for the storage modulus over the entire investigated temperature range, less agreement was found for the other modulus. This indicates that the order-disorder transition reflects changes on the molecular scale and slight modification of the physical network structure. To the authors' knowledge, this is the first time that this transition has been observed using these different rheological techniques.

Comparative rheological behavior of hyaluronan from bacterial and animal sources with cross-linked hyaluronan (hylan) in aqueous solution

Using a variety of rheological techniques, the behavior of hyaluronan (M(w) 0.8-2.2 x 10(6)), cross-linked hyaluronan (hylan) (M(w) 1.8-12.5 x 10(6)), and Healon (M(w) approximately 5 x 10(6)) (a proprietary hyaluronan) was studied over a large range of molecular weights. The object was to study the effect of the cross-links in hylan on the various rheological parameters, in comparison with linear hyaluronan. There are significant differences. The Huggins constant and the critical overlap parameter C*[eta] are considerably lower for hylan and an increase in moduli at low frequencies was observed for hylan compared with the hyaluronan samples at all molecular weights studied. The results point to a difference in structure in dilute solution for hylan due to the ability to form networks, which can be removed by pressure filtration. In contrast, we do not find an increase of the steady shear viscosity and elastic modulus at higher concentrations when a homogeneous entangled network is reached. We attribute this behavior to the semirigid character of the hyaluronan chain and to the predominance of entanglements over the cross-link points present in hylan in the semidilute domain. Due to the higher apparent molecular weights that are possible with hylan structures but not with the hyaluronans currently available, a wider range of applications can be achieved with hylans when viscoelasticity is required, particularly for the viscosupplementation of synovial fluid damaged by osteoarthritis.

Effects of a circuit weight training program on the body images of college students

OBJECTIVE

The present investigation examined the extent to which participation in a 6-week circuit-weight training program produced changes in participants' body images relative to a matched control group.

METHOD

The weight trainers consisted of 39 college students (27 women and 12 men). The control group of 39 individuals did not weight-train currently or within the past year. All participants were pre- and posttested on the Multidimensional Body Self-Relations Questionnaire, the Social Physique Anxiety Scale, and the Physical Self-Efficacy Scale. Weight trainers were also pre- and posttested on muscular strength and assessed on their motives for exercise.

RESULTS

The program successfully increased upper- and lower-body strength. In contrast to the comparison group, weight trainers had a significantly improved evaluation of their appearance, greater body satisfaction, reduced social physique anxiety, and enhanced physical self-efficacy. Outcomes were unrelated to the extent of concurrent aerobic exercise and largely unrelated to exercise motives.

DISCUSSION

Even a relatively brief weight training program can produce improvements in multiple aspects of body image. Further research should investigate weight training as an adjunct to psychosocial treatments of body dissatisfaction.

Microwear phenomena of ultrahigh molecular weight polyethylene cups and debris morphology related to gamma radiation dose in simulator study

Ultrahigh molecular weight polyethylene (PE) cups with 0, 2.5, 50, 100, and 150 Mrad radiation treatments were run in a hip simulator for comparison of the microwear phenomena on the cup surfaces with the corresponding debris morphology. In general, the size and frequency of the PE surface fibrils and the size of the retrieved PE debris decreased with increasing radiation dose. The fibril size and shape on the cup surfaces were well correlated with the radiation dose. The fibrillar shape and size were found to be proportional to the square root of the radiation dose. However, the trend for size and shape factors of the wear debris related to the radiation dose was weak at best. Thus, the morphology of the PE fibrils on the cup surfaces was more sensitive to variations in the radiation dose than the actual wear debris. The wear response appeared to be a three-step process, which was dependent on the formation of surface nodules or ripples, the teasing out of surface fibrils, and the toughness of the PE matrix in releasing a wear fibril to form a debris particle. The tougher PE became with increasing radiation dose, the harder it was for the PE fibrils to break out into wear particles.

Relative efficacy of an angiotensin II antagonist compared with other antihypertensive agents. Olmesartan medoxomil versus antihypertensives

OBJECTIVE

To compare the relative efficacy and safety of olmesartan medoxomil (OM) with atenolol, captopril and losartan in phase III trials on mild to severely hypertensive patients.

DESIGN

Multi-centre, randomized, double-blind, parallel group, with dose-titration studies lasting 12 or 24 weeks.

METHODS

Two studies respectively compared 10 mg OM once daily (o.d.) with: (1) 50 mg atenolol o.d. in moderate to severe hypertensives receiving 25 mg hydrochlorothiazide o.d. over 12 weeks; and (2) 50 mg losartan o.d. in mild to moderate hypertensives over 24 weeks, both with dose doubling at week4 if required. Study 3 compared 5 mg OM o.d. plus placebo o.d.with 12.5 mg captopril twice daily in mild to moderate hypertensives over 12 weeks, with dose doubling at weeks 4 and 8 if required. The primary outcome measure for all studies was the change from baseline to week 12 in trough mean sitting diastolic blood pressure (DBP). Safety was monitored throughout all studies.

RESULTS

(1) Atenolol and OM both reduced BP effectively in moderate to severe hypertensives. OM was significantly superior to: (2) losartan (95% confidence interval for baseline to week 12 change in DBP < 0, lower limit < -3.6 mmHg); and (3) captopril (95% confidence interval for baseline to week 12 change in DBP < 0, lower limit < -4.8 mmHg) in BP reduction for mild to moderate hypertensives. Treatment with OM was safe and well tolerated.

CONCLUSION

At the doses tested, olmesartan medoxomil o.d. is as effective as atenolol, and more effective than both losartan and captopril in reducing blood pressure in the hypertensive population.

Effects of A-P translation and rotation on the wear of UHMWPE in a total knee joint simulator

We developed a three-channel total knee joint simulator and studied the effect of tibial anterior-posterior translation and internal/external rotation on the wear of polyethylene tibial inserts in total knee replacements (Anatomic Graduated Component knees). The wear rate was the lowest in experiment (Exp.) 1, without translation and rotation [1.74 mg/million (mg/Mc) cycles]. In Exp. 2, with +/-5 degrees tibial rotation added, the wear rate increased to 10.6 mg/Mc. In Exp. 3, with rotation and -12 mm tibial translation added, the wear rate was 15.1 mg/Mc, whereas in Exp. 4, with rotation and +12 mm tibial translation, the wear rate was 18.7 mg/Mc. Internal/external rotation and anterior-posterior translation added a 6- to 11-fold increase in the wear rates of tibial knee inserts. The shapes of the tibial wear tracks were rectangular and the area of the track increased when rotation and translation were added.

Recombinant cytochrome rC557 obtained from Escherichia coli cells expressing a truncated Thermus thermophilus cycA gene. Heme inversion in an improperly matured protein

Cytochrome rC(557) is an improperly matured, dimeric cytochrome c obtained from expression of the "signal peptide-lacking" Thermus thermophilus cycA gene in the cytoplasm of Escherichia coli. It is characterized by its Q(00) (or alpha-) optical absorption band at 557 nm in the reduced form (Keightley, J. A., Sanders, D., Todaro, T. R., Pastuszyn, A., and Fee, J. A. (1998) J. Biol. Chem. 273, 12006-12016). We report results of a broad ranging, biochemical and spectral characterization of this protein that reveals the presence of a free vinyl group on the porphyrin and a disulfide bond between the protomers and supports His-Met ligation in both valence states of the iron. A 3-A resolution x-ray structure shows that, in comparison with the native protein, the heme moiety is rotated 180 degrees about its alpha,gamma-axis; cysteine 14 has formed a thioether bond with the 2-vinyl of pyrrole ring I instead of the 4-vinyl of pyrrole ring II, as occurs in the native protein; and a cysteine 11 from each protomer has formed an intermolecular disulfide bond. Numerous, minor perturbations exist within the structure of rC(557) in comparison with that of native protein, which result from heme inversion and protein-protein interactions across the dimer interface. The unusual spectral properties of rC(557) are rationalized in terms of this structure.

Effect of galactomannans on the thermal and rheological properties of sago starch

The thermal and rheological properties of sago starch have been studied in the presence of various concentrations of locust bean gum and guar gum of various molecular masses. At the concentrations studied (<1%) the galactomannans gave rise to only a very slight increase in the gelatinization temperature (up to 0.6 degrees C), and the gelatinization enthalpy remained constant within experimental error. For the low molecular mass galactomannans, depending on the concentration, the storage modulus, G', of the mixtures remained constant or actually decreased, and tan delta remained very low (0.01-0.03 at 0.1 Hz), indicating strong elastic gels. For the higher molecular mass samples G' increased significantly; however, the loss modulus, G' ', increased proportionally to a greater extent, and at 1% galactomannan tan delta was approximately 0.20 at 0.1 Hz, indicating a reduction in elastic character. The systems were shown to undergo phase separation, and the variations in rheological properties have been discussed in the context of their phase behavior and the relative rates of the phase separation and gelation processes. The presence of galactomannans significantly improved the freeze-thaw stability.

Replacement of the axial histidine ligand with imidazole in cytochrome c peroxidase. 1. Effects on structure

Replacement of the axial histidine ligand with exogenous imidazole has been accomplished in a number of heme protein mutants, where it often serves to complement the functional properties of the protein. In this paper, we describe the effects of pH and buffer ion on the crystal structure of the H175G mutant of cytochrome c peroxidase, in which the histidine tether between the heme and the protein backbone is replaced by bound imidazole. The structures show that imidazole can occupy the proximal H175G cavity under a number of experimental conditions, but that the details of the interaction with the protein and the coordination to the heme are markedly dependent on conditions. Replacement of the tethered histidine ligand with imidazole permits the heme to shift slightly in its pocket, allowing it to adopt either a planar or distally domed conformation. H175G crystallized from both high phosphate and imidazole concentrations exists as a novel, 5-coordinate phosphate bound state, in which the proximal imidazole is dissociated and the distal phosphate is coordinated to the iron. To accommodate this bound phosphate, the side chains of His-52 and Asn-82 alter their positions and a significant conformational change in the surrounding protein backbone occurs. In the absence of phosphate, imidazole binds to the proximal H175G cavity in a pH-dependent fashion. At pH 7, imidazole is directly coordinated to the heme (d(Fe--Im) = 2.0 A) with a nearby distal water (d(Fe--HOH) = 2.4 A). This is similar to the structure of WT CCP except that the iron lies closer in the heme plane, and the hydrogen bond between imidazole and Asp-235 (d(Im--Asp) = 3.1 A) is longer than for WT CCP (d(His--Asp) = 2.9 A). As the pH is dropped to 5, imidazole dissociates from the heme (d(Fe--Im) = 2.9 A), but remains in the proximal cavity where it is strongly hydrogen bonded to Asp-235 (d(Im--Asp) = 2.8 A). In addition, the heme is significantly domed toward the distal pocket where it may coordinate a water molecule. Finally, the structure of H175G/Im, pH 6, at low temperature (100 K) is very similar to that at room temperature, except that the water above the distal heme face is not present. This study concludes that steric restrictions imposed by the covalently tethered histidine restrain the heme and its ligand coordination from distortions that would arise in the absence of the restricted tether. Coupled with the functional and spectroscopic properties described in the following paper in this issue, these structures help to illustrate how the delicate and critical interactions between protein, ligand, and metal modulate the function of heme enzymes.

Cloning and characterization of the pnb genes, encoding enzymes for 4-nitrobenzoate catabolism in Pseudomonas putida TW3

Pseudomonas putida strain TW3 is able to metabolize 4-nitrotoluene via 4-nitrobenzoate (4NBen) and 3, 4-dihydroxybenzoic acid (protocatechuate [PCA]) to central metabolites. We have cloned, sequenced, and characterized a 6-kbp fragment of TW3 DNA which contains five genes, two of which encode the enzymes involved in the catabolism of 4NBen to PCA. In order, they encode a 4NBen reductase (PnbA) which is responsible for catalyzing the direct reduction of 4NBen to 4-hydroxylaminobenzoate with the oxidation of 2 mol of NADH per mol of 4NBen, a reductase-like enzyme (Orf1) which appears to have no function in the pathway, a regulator protein (PnbR) of the LysR family, a 4-hydroxylaminobenzoate lyase (PnbB) which catalyzes the conversion of 4-hydroxylaminobenzoate to PCA and ammonium, and a second lyase-like enzyme (Orf2) which is closely associated with pnbB but appears to have no function in the pathway. The central pnbR gene is transcribed in the opposite direction to the other four genes. These genes complete the characterization of the whole pathway of 4-nitrotoluene catabolism to the ring cleavage substrate PCA in P. putida strain TW3.

Damage to cobalt-chromium surfaces during arthroscopy of total knee replacements

BACKGROUND

It has been stated that care must be taken not to scratch the metal components during total knee arthroscopy; however, this concern has not been studied. Clinical observation during arthroscopy of total knee replacements suggested the possibility of damage to the femoral component by the arthroscopic cannula; therefore, a bench test was performed to study this potential risk.

METHODS

Cobalt-chromium femoral components were tested to determine the surface damage that resulted from moving a stainless-steel arthroscopic cannula and a plastic arthroscopic cannula across the components under a variety of applied loads. Scanning electron microscopy and surface-roughness measurements of the prosthetic surface were used to evaluate the damage.

RESULTS

The stainless-steel cannula produced observable alterations to the surface of the femoral component at loads as small as 8 N. The majority of these alterations were deposits of stainless steel from the cannula onto the component. The plastic cannula did not appear to produce alterations on the component surface. Surface roughness increased with increasing loading of the stainless-steel cannula, but there was no noticeable change with increasing loading of the plastic cannula. These forces did, however, severely damage some parts of the plastic cannula.

CONCLUSIONS

Alterations to the surface of cobalt-chromium femoral components can occur during arthroscopy with stainless-steel cannulae but not with plastic cannulae. The results of this study support a recommendation to use plastic cannulae during arthroscopy of total knee replacements.

CLINICAL RELEVANCE

Arthroscopy of total knee replacements is increasing in the clinical setting, and damage to the prosthesis should be avoided whenever possible. This study provides evidence that damage to the femoral component is possible with a stainless-steel cannula and that use of a plastic cannula may reduce this risk.

areCBA is an operon in Acinetobacter sp. strain ADP1 and Is controlled by AreR, a sigma(54)-dependent regulator

The areCBA genes in Acinetobacter sp. strain ADP1, determining growth on benzyl alkanoates, are shown to be transcribed as a single operon and regulated by areR, which encodes a regulatory protein of the NtrC/XylR family. Assays of the Are enzymes and of two insertions of lacZ as a reporter gene have shown that the operon is induced by benzyl acetate, benzyl alcohol, and benzaldehyde, as well as 2- and 4-hydroxybenzyl acetates and benzyl propionate and butyrate. Two adjacent sites of transcriptional initiation were 97 and 96 bp upstream of the start codon for areC, near a sigma(54)-dependent -12, -24 promoter. Inactivation of areR and rpoN (for RNA polymerase sigma(54)) drastically reduced growth rates on the Are substrates and induction of the operon.

On the interaction of the vanadyl(IV) cation with lactose: inhibition effects of vanadyl(IV)/monosaccharide and disaccharide complexes upon alkaline phosphatase activity

A new vanadyl(IV) complex of the disaccharide lactose was obtained in aqueous solution at pH = 13. The sodium salt of the complex, of composition Na4[VO(lactose)2].3H2O, has been characterized by elemental analysis and by ultraviolet-visible, diffuse reflectance, and infrared spectroscopies. Its magnetic susceptibility and thermal behavior were also investigated. The inhibitory effect on alkaline phosphatase activity was tested for this compound as well as for the vanadyl(IV) complexes with maltose, sucrose, glucose, fructose, and galactose. For comparative purposes, the free ligands and the vanadyl(IV) cation were also studied. The free sugars and the sucrose/VO complex exhibited the lowest inhibitory effect. Lactose-VO, maltose-VO, and the free VO2+ cation showed an intermediate inhibition potential, whereas the monosaccharide/VO complexes appeared as the most potent inhibitory agents.

nag genes of Ralstonia (formerly Pseudomonas) sp. strain U2 encoding enzymes for gentisate catabolism

Ralstonia sp. strain U2 metabolizes naphthalene via gentisate to central metabolites. We have cloned and sequenced a 21.6-kb region spanning the nag genes. Upstream of the pathway genes are nagY, homologous to chemotaxis proteins, and nagR, a regulatory gene of the LysR family. Divergently transcribed from nagR are the genes for conversion of naphthalene to gentisate (nagAaGHAbAcAdBFCQED) (S. L. Fuenmayor, M. Wild, A. L. Boyes, and P. A. Williams, J. Bacteriol. 180:2522-2530, 1998), which except for the insertion of nagGH, encoding the salicylate 5-hydroxylase, are homologous to and in the same order as the genes in the classical upper pathway operon described for conversion of naphthalene to salicylate found in the NAH7 plasmid of Pseudomonas putida PpG7. Downstream of nahD is a cluster of genes (nagJIKLMN) which are probably cotranscribed with nagAaGHAbAcAdBFCQED as a single large operon. By cloning into expression vectors and by biochemical assays, three of these genes (nagIKL) have been shown to encode the enzymes involved in the further catabolism of gentisate to fumarate and pyruvate. NagI is a gentisate 1,2-dioxygenase which converts gentisate to maleylpyruvate and is also able to catalyze the oxidation of some substituted gentisates. NagL is a reduced glutathione-dependent maleylpyruvate isomerase catalyzing the isomerization of maleylpyruvate to fumarylpyruvate. NagK is a fumarylpyruvate hydrolase which hydrolyzes fumarylpyruvate to fumarate and pyruvate. The three other genes (nagJMN) have also been cloned and overexpressed, but no biochemical activities have been attributed to them. NagJ is homologous to a glutathione S-transferase, and NagM and NagN are proteins homologous to each other and to other proteins of unknown function. Downstream of the operon is a partial sequence with homology to a transposase.

Integrity of thermus thermophilus cytochrome c552 synthesized by Escherichia coli cells expressing the host-specific cytochrome c maturation genes, ccmABCDEFGH: biochemical, spectral, and structural characterization of the recombinant protein

We describe the design of Escherichia coli cells that synthesize a structurally perfect, recombinant cytochrome c from the Thermus thermophilus cytochrome c552 gene. Key features are (1) construction of a plasmid-borne, chimeric cycA gene encoding an Escherichia coli-compatible, N-terminal signal sequence (MetLysIleSerIleTyrAlaThrLeu AlaAlaLeuSerLeuAlaLeuProAlaGlyAla) followed by the amino acid sequence of mature Thermus cytochrome c552; and (2) coexpression of the chimeric cycA gene with plasmid-borne, host-specific cytochrome c maturation genes (ccmABCDEFGH). Approximately 1 mg of purified protein is obtained from 1 L of culture medium. The recombinant protein, cytochrome rsC552, and native cytochrome c552 have identical redox potentials and are equally active as electron transfer substrates toward cytochrome ba3, a Thermus heme-copper oxidase. Native and recombinant cytochromes c were compared and found to be identical using circular dichroism, optical absorption, resonance Raman, and 500 MHz 1H-NMR spectroscopies. The 1.7 A resolution X-ray crystallographic structure of the recombinant protein was determined and is indistinguishable from that reported for the native protein (Than, ME, Hof P, Huber R, Bourenkov GP, Bartunik HD, Buse G, Soulimane T, 1997, J Mol Biol 271:629-644). This approach may be generally useful for expression of alien cytochrome c genes in E. coli.

Characterization of new oxovanadium(IV) complexes of saccharides

Oxovanadium(IV) complexes of the monosaccharides D- and L-arabinose, D-galactose, D-mannose, D-lyxose, D-xylose and the disaccharide maltose were obtained in aqueous solutions at pH 13. Their sodium salts were precipitated with absolute ethanol and characterized by UV-vis spectroscopy (absorption and reflectance), thermo-analytical (TG and DTA) data, magnetic susceptibility measurements and IR-spectroscopy. All the complexes were found to be mononuclear, possessing the VO2+ moiety. The IR spectra were analyzed and discussed in detail allowing one to determine the characteristics of the metal-to-ligand interactions.

Quantum mechanical interpretation of nitrite reduction by cytochrome cd1 nitrite reductase from Paracoccus pantotrophus

The reduction of nitrite to nitric oxide in respiratory denitrification is catalyzed by a cytochrome cd(1) nitrite reductase in Paracoccus pantotrophus (formerly known as Thiosphaera pantotropha LMD 92.63). High-resolution structures are available for the fully oxidized [Fülöp, V., Moir, J. W., Ferguson, S. J., and Hajdu, J. (1995) Cell 81, 369-377; Baker, S. C., Saunders, N. F., Willis, A. C., Ferguson, S. J., Hajdu, J., and Fülöp, V. (1997) J. Mol. Biol. 269, 440-455] and fully reduced forms of this enzyme, as well as for various intermediates in its catalytic cycle [Williams, P. A., Fülöp, V., Garman, E. F., Saunders, N. F., Ferguson, S. J., and Hajdu, J. (1997) Nature 389, 406-412]. On the basis of these structures, quantum mechanical techniques (QM), including density functional methods (DFT), were combined with simulated annealing (SA) and molecular mechanics techniques (MM) to calculate the electronic distribution of molecular orbitals in the active site during catalysis. The results show likely trajectories for electrons, protons, substrates, and products in the process of nitrite reduction, and offer an interpretation of the reaction mechanism. The calculations indicate that the redox state of the d(1) heme and charges on two histidines in the active site orchestrate catalysis locally. Binding of nitrite to the reduced iron is followed by proton transfer from His345 and His388 to one of the oxygens of nitrite, creating a water molecule and an [Fe(II)-NO(+)] complex. Valence isomerization within this complex gives [Fe(III)-NO]. The release of NO from the ferric iron is influenced by the protonation state of His345 and His388, and by the orientation of NO on the d(1) heme. Return of Tyr25 to a hydrogen-bonding position between His345 and His388 facilitates product release, but a rebinding of Tyr25 to the oxidized iron may be bypassed in steady-state catalysis.

Microsomal cytochrome P450 2C5: comparison to microbial P450s and unique features

Although microsomal P450s represent the majority of P450s, only microbial P450s have been amenable to crystal structure solution. We have recently solved the first crystal structure of a microsomal P450, 2C5, a progesterone hydroxylase from rabbit. We discuss the features of the protein in common with existing structures of microbial P450s and limitations of homology modeling mammalian P450s based on the microbial structures. Unique features involving membrane, substrate and cytochrome P450 reductase interactions are also discussed.

The effect of hydroxyl radicals on the rheological performance of hylan and hyaluronan

Shear flow, dynamic oscillation and extensional viscosity measurements were used to compare the rheological performance of several hylan samples (M(v) 1.6, 3.2, 3.7, 4.7 and 5.6x10(6)) and hyaluronan (M(v) 1.4 and 1.8x10(6)) before and after hydroxyl radicals (*OH) induced degradation. It was found that the higher molecular weight cross-linked structure of hylan was more resistant to degradation than hyaluronan and that this superior stability was reflected in various rheological parameters. The *OH degradation of the initial hylan and hyaluronan samples produced a range of polysaccharides based on hylan and hyaluronan with molecular weight covering a range from 0.5-5.6x10(6). The rheological parameters associated with the polysaccharides could then also be studied. Zero shear values of the complex viscosity (eta*), dynamic viscosity (eta') and shear viscosity (eta) were calculated using the method of Morris(1) and shown to approach the same value at zero shear or frequency. An adaptation of the method of Gibbs et al. gave a 'master curve' for the storage and loss modulus of hyaluronan and hylan, which encompasses a 10-fold molecular weight and a 5-fold concentration variation. In all instances for hylan, the storage modulus predominates over the loss modulus, whereas for hyaluronan, the reverse is true, demonstrating the greater elasticity of hylan throughout the whole experimental range of molecular weights and concentrations.

Cloning and expression of ntnD, encoding a novel NAD(P)(+)-independent 4-nitrobenzyl alcohol dehydrogenase from Pseudomonas sp. Strain TW3

Pseudomonas sp. strain TW3 is able to metabolize 4-nitrotoluene to 4-nitrobenzoate and toluene to benzoate aerobically via a route analogous to the upper pathway of the TOL plasmids. We report the cloning and characterization of a benzyl alcohol dehydrogenase gene (ntnD) which encodes the enzyme for the catabolism of 4-nitrobenzyl alcohol and benzyl alcohol to 4-nitrobenzaldehyde and benzaldehyde, respectively. The gene is located downstream of the previously reported ntn gene cluster. NtnD bears no similarity to the analogous TOL plasmid XylB (benzyl alcohol dehydrogenase) protein either in its biochemistry, being NAD(P)(+) independent and requiring assay via dye-linked electron transfer, or in its deduced amino acid sequence. It does, however, have significant similarity in its amino acid sequence to other NAD(P)(+)-independent alcohol dehydrogenases and contains signature patterns characteristic of type III flavin adenine dinucleotide-dependent alcohol oxidases. Reverse transcription-PCR demonstrated that ntnD is transcribed during growth on 4-nitrotoluene, although apparently not as part of the same transcript as the other ntn genes. The substrate specificity of the enzyme expressed from the cloned and overexpressed gene was similar to the activity expressed from strain TW3 grown on 4-nitrotoluene, providing evidence that ntnD is the previously unidentified gene in the pathway of 4-nitrotoluene catabolism. Examination of the 14.8-kb region around the ntn genes suggests that one or more recombination events have been involved in the formation of their current organization.

Particles released from the Gyro C1E3 during simulated extracorporeal circulation

Evaluation of released particles from the blood pump during extracorporeal circulation is an important aspect because the particles may cause microembolism. The Gyro C1E3 is a centrifugal blood pump that has an impeller suspended by double pivot bearings inside the housing; therefore, it is important to evaluate the released particles. The C1E3 was driven for 14 days to simulate clinical left ventricular assist device (LVAD) and percutaneous cardiopulmonary support (PCPS). Also, a roller pump was driven for 2 days as a comparison. Released particles were weighed and examined by SEM. After 14 days of pumping, the particles from the C1E3 were 238.6 microg in an LVAD condition. The particles with the roller pump were 270.2 microg after only 2 days. Average particle sizes with the roller pump and C1E3 were 3.7 and 0.6 microm, respectively. These results suggest that the Gyro C1E3 substantially reduces the risk of microembolism from released particles.

Synthesis, characterization and bioactivity of a new VO2+/aspirin complex

A new VO2+ complex with salicylic acid acetate (Aspirin) of formula C18H18Cl2O12V2 was synthesized and characterized. Its biological effects upon cell proliferation, differentiation and promotion of tyrosine protein phosphorylation have been tested in two lines of osteoblast-like cells in culture.