Localization of the active site of type II dehydroquinases. Identification of a common arginine-containing motif in the two classes of dehydroquinases

A novel method based on electrospray mass spectrometry (Krell, T., Pitt, A. R., and Coggins, J. R. (1995) FEBS Lett. 360, 93-96) has been used to localize active site residues in the type I and type II dehydroquinases. Both enzymes have essential hyper-reactive arginine residues, and the type II enzymes have an essential tyrosine residue. The essential hyper-reactive Arg-23 of the Streptomyces coelicolor type II enzyme has been replaced by lysine, glutamine, and alanine residues. The mutant enzymes were purified and shown by CD spectroscopy to be structurally similar to the wild-type enzyme. All three mutant enzymes were much less active, for example the kcat of the R23A mutant was 30,000-fold reduced. The mutants all had reduced Km values, indicating stronger substrate binding, which was confirmed by isothermal titration calorimetry experiments. A role for Arg-23 in the stabilization of a carbanion intermediate is proposed. Comparison of the amino acid sequence around the hyper-reactive arginine residues of the two classes of enzymes indicates that there is a conserved structural motif that might reflect a common substrate binding fold at the active center of these two classes of enzyme.

The effect of a non-absorbable fat substitute, sucrose polyester, on gastrointestinal function

OBJECTIVES

To assess the effects of a single dose of a non-absorbable fat substitute, sucrose polyester, on gastrointestinal function.

METHODS

The effects of 50 g of sucrose polyester taken as a single drink on gastric emptying, small bowel transit time (SBTT), whole gut transit time (WGTT) and faecal weight compared with a control fat were examined in double-blind studies. The effect of sucrose polyester on gallbladder ejection fraction and gastrointestinal hormones was also assessed.

RESULTS

Sucrose polyester was found to accelerate gastric emptying significantly (98.33 +/- 71.0 vs. 112.92 +/- 82.0 min, P = 0.042) but to slow SBTT (153.75 +/- 36.25 vs. 128.75 +/- 47.39 min. P = 0.006). A trend to faster WGTT (37.47 +/- 15.61 vs. 46.63 +/- 20.65 h) and increased faecal weight was observed (453.33 +/- 122.05 vs. 395.0 +/- 107.85 g/48 h), but this did not reach statistical significance. There was a striking reduction in gallbladder ejection fraction with sucrose polyester (21.69 +/- 25.32 vs. 45.27 +/- 27.67%), P = 0.039) and a corresponding significant decrease in the release of cholecystokinin. Lower levels of motilin and enteroglucagon were also observed.

CONCLUSIONS

Sucrose polyester has significant effects on gastrointestinal transit, gallbladder contraction and gastrointestinal hormones. These effects can be explained on the basis of decreased luminal products of digestion and may have implications for the widespread use of sucrose polyester as a fat substitute.

Analysis of the structural stability of the multidomain enzyme flavocytochrome P-450 BM3

The unfolding and refolding of flavocytochrome P-450 BM3 and its constituent haem and flavin domains have been analysed, using guanidinium chloride (GdnHCl) as a denaturant. Enzyme activities are lost at GdnHCl concentrations too low to cause major changes in secondary structure (0.1-0.5 M). The losses are primarily due to time-dependent FMN removal. Fluorescence and visible CD spectroscopies show that FMN dissociation is complete by 0.7 M GdnHCl, whereas FAD removal is complete by 1.5 M GdnHCl. Limited regain of activity is achieved by dilution of enzyme from solutions of < or = 0.75 M GdnHCl into fresh buffer. Supplementation of GdnHCl-free assay media with flavins (FAD and FMN) causes small additional regains in flavin domain (cytochrome-c reductase) activity lost at low [GdnHCl]. However, flavin addition during the denaturation step affords greater protection against inactivation, suggesting that conformational changes may occur subsequent to flavin loss and that these changes are not readily reversed on dilution of GdnHCl. Loss of catalytically competent haem ligation occurs over the same [GdnHCl] range for P-450 BM3 and its haem domain. In both cases, the 'denatured' P-420 form accumulates in the reduced/carbon monoxide-bound visible spectrum from 0.5 to 2 M GdnHCl. Secondary structure loss also occurs over similar [GdnHCl] ranges for P-450 BM3 and its two domains (80-90% lost from 0.5-3 M GdnHCl), indicating that there is little mutual stabilisation of domains in the holoenzyme. Differential scanning calorimetry measurements support this conclusion, but show that the haem domain is more thermostable than the flavin domain.

Posttransplant lymphoproliferative disease in pediatric liver transplantation. Interplay between primary Epstein-Barr virus infection and immunosuppression

The incidence, risk factors, and outcome of posttransplant lymphoproliferative disease (PTLD) were examined for 298 children undergoing liver transplantation. The overall incidence of PTLD was 8.4% (25 of 298). Intensity of immunosuppression was found to be a major risk factor for the development of PTLD. Cyclosporine and tacrolimus when used as primary immunosuppression were associated with the development of PTLD in 4.3% and 6.6% of cases (P=NS). OKT3 and tacrolimus, when used as rescue therapy for steroid-resistant rejection, were associated with a comparable increase in the risk of developing PTLD (10.9% and 11.1%, P=NS). Patients requiring both OKT3 and tacrolimus to treat refractory rejection were at significantly increased risk for PTLD (28.1% vs. 4.3% or 6.6%, P<0.0001). PTLD was more common in patients who received transplants for Langerhans cell histiocytosis relative to other indications for transplantation (66% vs. 8.4%, P=0.0005). The data also support an association between primary Epstein-Barr virus (EBV) infections following transplantation and the development of PTLD. While only three patients were EBV seropositive before transplantation (14%), 19 patients were EBV seropositive at the time of diagnosis of PTLD (90%), confirming a high incidence of primary EBV infections in patients with PTLD (21 patients had both pre- and posttransplant EBV serologies). In this series, PTLD was associated with a mortality rate of 60%, and 12 of the 15 patients who died had persistent tumor at the time of death. Five of the 13 patients rendered disease-free developed ductopenic rejection. Of the four with severe liver dysfunction, two have undergone successful retransplantation and are alive without evidence of PTLD. In conclusion, intense immunosuppression using OKT3 and tacrolimus as rescue agents was associated with a significant increase in the incidence of PTLD. Primary EBV infection after transplantation further accentuated this risk. Independent of these risk factors, patients with Langerhans cell histiocytosis were at significantly increased risk for PTLD. The identification of high-risk patients should allow the development of protocols to screen patients for primary EBV infections and early indications of PTLD, as well as the institution of preemptive antiviral and antitumor therapies.

Phosphoglycerate mutase from Schizosaccharomyces pombe: development of an expression system and characterisation of three histidine mutants of the enzyme

The small, monomeric, phosphoglycerate mutase (PGAM) from Schizosaccharomyces pombe has been overexpressed in a strain of Saccharomyces cerevisiae in which the gene encoding PGAM has been deleted, with a yield of purified enzyme of 10-15 mg per litre cell culture. Three mutants in which histidine residues in S. pombe PGAM have been substituted by glutamine have been purified and characterised. Two mutants (H151Q and H196Q) have kinetic and structural properties very similar to wild-type enzyme, consistent with the proposed location of these (non-conserved) histidines on the surface of the enzyme. The third mutant (H163Q) involving a histidine thought to be part of the active site has greatly reduced mutase and phosphatase activities. Mass spectrometry shows that the phosphorylated form of the H163Q is several 100-times more stable towards hydrolysis than the phosphorylated form of wild-type enzyme. The H163Q mutant appears to be structurally quite distinct from wild-type enzyme. 600 MHz 1D proton NMR spectra of good quality have been obtained for wild-type enzyme and the H151Q and H196Q mutants.

Airway foreign bodies

The removal of airway foreign bodies can be challenging even for the most experienced endoscopist. A familiarity with and working knowledge of older time-tested techniques and instrumentation as well as of the newer rigid and flexible fiberoptic equipment is essential for all who desire to accept these challenging situations. Each instrument has inherent advantages, disadvantages, and limitations in certain situations. Occasionally, a foreign body may be removed more safely through open surgical procedures. A knowledge of the lessons learned and techniques developed by pioneering endoscopists coupled with continuing practice of different endoscopy techniques with a variety of instrumentation will prepare the endoscopist to handle unusual foreign body dilemmas with greater skill and safety.

Attenuated Salmonella typhimurium containing interleukin-2 decreases MC-38 hepatic metastases: a novel anti-tumor agent

Currently, there is no long-term effective treatment for unresectable hepatic malignancies. Salmonella sp. are known to naturally track to the liver during active infection. To develop a biological vector for delivery of Interleukin-2 (IL-2) to the liver for anti-tumor purposes, the avirulent and highly immunogenic chi 4550 strain of Salmonella typhimurium was used as a vector for IL-2. The gene for human IL-2 was cloned into plasmid pYA292 (renamed pIL-2) and inserted into the attenuated Salmonella typhimurium and renamed [chi 4550 (pIL-2)]. This transformant was found to produced biologically active IL-2 demonstrated by NK cell activation in a 4 hour chromium release cytotoxicity assay. To determine anti-tumor potential, MCA-38 murine adenocarcinoma cells were injected intrasplenically into C57BL/6 mice to produce hepatic metastases and metastases were subsequently enumerated after 12 days. Statistical significance was determined by ANOVA with Fisher's test for significance. Hepatic metastases enumerated by blinded observers revealed that the mean number of metastases was 106.4 in control mice, 103.7 in mice gavage fed attenuated salmonella without IL-2 [chi 4550(pYA292)], and 44.3 in mice fed the chi 4550(pIL2); (ANOVA: p < 0.01). Culture of livers and spleens in mice administered a single gavage dose of salmonella demonstrated persistent colonization for up to 4 weeks. No observable toxicity was seen to either IL-2 or salmonella. These studies demonstrate that the chi 4550(pIL2) is a novel form of in vivo biotherapy which produces biologically active IL-2 and employs the oral route of administration to stimulate an immune response against malignancy in the liver.

Cytotoxicity of prion protein peptide (PrP106-126) differs in mechanism from the cytotoxic activity of the Alzheimer's disease amyloid peptide, A beta 25-35

The abnormal form of the prion protein (PrPSc), a synthetic prion protein peptide fragment (PrP106-126) and fragments of the Alzheimer's protein precursor, APP, have been shown to be cytotoxic in vitro. We have used synchronous, clonal cell models originally developed to study the toxicity of the Alzheimer's disease amyloid peptide, A beta 25-35, to investigate the actions of PrP peptides. We found that the cytotoxicity of the PrP106-126 depends on its state of aggregation and the cellular expression of PrPc, and is independent of a loss of MTT reduction activity in the absence of cell death associated with the cellular effects of A beta 25-35. These factors may play a role in the lesion specificity of different pathological phenotypes of prion-protein related diseases.

An analysis of the conformational changes that accompany the activation and inhibition of gelatinase A

The latent precursors of the matrix metalloproteinases (MMPs) are converted by (4-aminophenylmercuric)acetate to active forms that lose their propeptide as a result of autolysis. C.D. and an active site mutant of progelatinase A (MMP2) were used to demonstrate that, although propeptide removal is accompanied by a decrease in the enzyme's beta-sheet content, the initial activation is achieved with only minor modifications to the conformation. Mixing activated gelatinase A with the natural inhibitor, TIMP-1, resulted in conformational changes that were absent when a synthetic inhibitor was used. The relevance of these results to MMP activation and inhibition is discussed.

The failure of triage criteria to identify geriatric patients with trauma: results from the Florida Trauma Triage Study

Since 1990, Florida has used a uniform set of eight triage criteria, known as the trauma scorecard, for triaging adult patients with trauma to state-approved trauma centers. If any one of the eight criteria are met, paramedics classify the patient as a "trauma alert" and transport to a state-approved trauma center. Widespread concern within the trauma care community that the scorecard was not providing an effective tool for adult trauma triage, particularly for older adults, was a motivating force for conducting an evaluation of the trauma scorecard's performance. Thus, the Florida Department of Health and Rehabilitative Services, Office of Emergency Medical Services initiated a research effort to assess the effectiveness of the state-adopted trauma triage criteria for adults, giving special attention to geriatric trauma. The results of the Florida Trauma Triage Study indicate that the eight triage criteria comprising the trauma scorecard produce unacceptable levels of undertriage in elderly patients (age 55 years or older) with life-threatening injuries.

Intracellular pressure is a motive force for cell motion in Amoeba proteus

The cortical filament layer of free-living amoebae contains concentrated actomyosin, suggesting that it can contract and produce an internal hydrostatic pressure. We report here on direct and dynamic intracellular pressure (P(ic)) measurements in Amoeba proteus made using the servo-null technique. In resting apolar A. proteus, P(ic) increased while the cells remained immobile and at apparently constant volume. P(ic) then decreased approximately coincident with pseudopod formation. There was a positive correlation between P(ic) at the onset of movement and the rate of pseudopod formation. These results are the first direct evidence that hydrostatic pressure may be a motive force for cell motion. We postulate that contractile elements in the amoeba's cortical layer contract and increase P(ic) and that this P(ic) is utilized to overcome the viscous flow resistance of the intracellular contents during pseudopod formation.

Kinetics of acid-mediated disassembly of the B subunit pentamer of Escherichia coli heat-labile enterotoxin. Molecular basis of pH stability

The B-subunit pentamer of Escherichia coli heat-labile enterotoxin (EtxB) is highly stable, maintaining its quaternary structure in a range of conditions that would normally be expected to cause protein denaturation. In this paper the structural stability of EtxB has been studied as a function of pH by electrophoretic, immunochemical, and spectroscopic techniques. Disassembly of the cyclic pentameric structure of human EtxB occurs only below pH 2. As determined by changes in intrinsic fluorescence this process follows first-order kinetics, with the rate constant for disassembly being proportional to the square of the H+ ion concentration, and with an activation energy of 155 kJ mol-1. A C-terminal deletion mutant, hEtxB214, similarly shows first-order kinetics for disassembly but with a higher pH threshold, resulting in disassembly being seen at pH 3.4 and below. These findings are consistent with the rate-limiting step for disassembly of human EtxB being the simultaneous disruption of two interfaces by protonation of two C-terminal carboxylates. By comparison, disassembly of the B-subunit of cholera toxin (CtxB), a protein which shows 80% sequence identity with EtxB, exhibits a much lower stability to acid conditions; with disassembly of CtxB occurring below pH 3.9, with an activation energy of 81 kJ mol-1. Reasons for the observed differences in acid stability are discussed, and the implications of these findings to the development of oral vaccines using EtxB and CtxB are considered.

Unilateral endoscopic supraglottoplasty for severe laryngomalacia

OBJECTIVE

To evaluate the effectiveness of unilateral supraglottoplasty in the treatment of children with severe laryngomalacia.

DESIGN

Retrospective study.

SETTING

Pediatric tertiary referral center.

PATIENTS

Eighteen children with severe laryngomalacia. Indications for surgical intervention were obstructive apnea, failure to thrive, cyanosis, and/or cor pulmonale.

INTERVENTIONS

Unilateral carbon dioxide laser removal of redundant supraglottic tissue (supraglottoplasty).

OUTCOME MEASURES

Evaluation of relief of symptoms, need for subsequent contralateral procedure, and incidence of complications.

RESULTS

Three patients required treatment of the opposite side at a later date. There were no complications. Obstructive apnea and weight gain improved in all.

CONCLUSIONS

Unilateral supraglottoplasty can be used to treat severe laryngomalacia in most patients. A small percentage of patients will subsequently require a contralateral procedure. Unilateral supraglottoplasty may have less risk of complications than bilateral supraglottoplasty.

NADPH oxidase activity of cytochrome P-450 BM3 and its constituent reductase domain

Cytochrome P-450 BM3 from Bacillus megaterium catalyses NADPH oxidation in the absence of added substrate. This activity is also associated with the independently expressed flavin-containing reductase domain of the protein. The rates of these activities are more than two orders of magnitude lower than those in the presence of fatty acid P-450 substrates or artificial electron acceptors. Electrons derived from NADPH in this fashion are transferred onto oxygen, generating superoxide (O2-) anions. The formation of these active oxygen species is detectable by luminometry and the chemiluminescence can be inhibited through the addition of superoxide dismutase (but not catalase). This activity is reminiscent of the microbicidal NADPH oxidase activity associated with neutrophils and other leukocyte blood cell types. Diphenyliodonium, a potent inhibitor of the neutrophil NADPH oxidase, effectively inhibits fatty acid hydroxylase and electron transferase activities catalysed by P-450 BM3 and its reductase domain. CD studies on the native and NADPH-reduced P-450 BM3 and BM3 reductase indicate that no secondary structural alteration is caused by pre-incubation with the reductant. Therefore, the previously recognised reversible time-dependent inactivation of P-450 BM3 by NADPH may be attributed to the NADPH oxidase activity associated with the reductase domain of the enzyme.

Endoscopic balloon dilatation of duodenal strictures in Crohn's disease

Endoscopic balloon dilatation of oesophageal and colonic strictures is now widely performed. Duodenal strictures due to Crohn's disease represent a difficult clinical problem as surgical intervention is a major undertaking and recurrences are common. We describe endoscopic balloon dilatation in three patients with obstructive symptoms from duodenal strictures due to Crohn's disease. The procedure appeared safe, was well tolerated and resulted in an excellent symptomatic response. This method is particularly suitable for short duodenal strictures and avoids the need for surgical intervention in this difficult group of patients.

Conformational changes induced by DNA binding of NF-kappa B

The transcription factor NF-kappa B makes extensive contacts with its recognition site over one complete turn of the double helix. Structural transitions, in both protein and DNA, that accompany formation of the DNA-protein complex were analysed by proteinase sensitivity and circular dichroism (CD) spectroscopy. In the absence of DNA chymotrypsin cleaved p50 after residues Y60 and N78, while proteinase K cleaved p50 after residues S74 and Q180. Previous experiments had indicated that trypsin cleaved p50 after K77. Cleavages after Y60, S74, K77 and N78 were blocked in the presence of bound DNA, whereas cleavage after Q180 was enhanced. Y60, S74, K77 and N78 are all located in the p50 N-terminal domain AB loop, whereas Q180 is located in the mainly alpha-helical region between p50 N-terminal domain beta-strands G' and H. As only Y60 makes direct contact with the DNA it is likely that the AB loop is highly unstructured in the absence of DNA, but is held in a rigid, proteinase-resistant structure by bound DNA. These conclusions were supported by CD spectroscopic studies of recombinant p50 and p65 homodimers, which indicated that both species changed conformation when binding DNA. Examination of the near UV CD spectra revealed that with some DNA sequences the bound and free forms of the DNA assumed different conformations. While this was evident for a fully symmetrical, high affinity recognition site DNA, it was not apparent with less tightly bound DNA.

The DvA-1 polyprotein of the parasitic nematode Dictyocaulus viviparus. A small helix-rich lipid-binding protein

DNA encoding a single unit of the DvA-1 polyprotein of the parasitic nematode Dictyocaulus viviparus was isolated and the polypeptide ("rDvA-1L") expressed in Escherichia coli, to give a protein showing high binding affinity for fatty acids and retinoids. Fluorescent fatty acid probes show substantial changes in emission spectrum in the presence of rDvA-1L, which can be reversed by fatty acids (oleic, palmitic, stearic, arachidonic) and retinoids, but not by tryptophan, squalene, or cholesterol. Moreover, changes in intrinsic fluorescence of retinol or retinoic acid confirm a retinoid binding activity. Fluorescence titration experiments indicate stoichiometric binding to a single protein site per monomer unit with affinities (Kd) in the range 3 x 10(-8) M for 11-((5-dimethylaminonaphthalene-1-sulfonyl)amino)undecanoic acid, and by competition, 5 x 10(-8) M for oleic acid. The extreme blue shift of bound fluorescent fatty acid suggests an unusually low polarity for the protein binding site. The emission spectrum of the single tryptophan of rDvA-1L indicates that it is deeply buried in a nonpolar environment, and its spectrum is unaffected by ligand binding. Far UV circular dichroism of rDvA-1L reveals a high alpha-helix content (53%). Differential scanning calorimetry studies indicate that rDvA-1L is highly stable (T(m) approximately 98 degrees C), refolding efficiently following thermal denaturation. DvA-1 therefore represents an example of a new class of lipid binding protein, and is the first product of a polyprotein with this activity to be described.

Control of cell volume in oocytes and eggs from Xenopus laevis

The mechanism by which Xenopus laevis oocytes and eggs survive in hypotonic media was investigated by measuring cell volume (Vc) and intracellular pressure (P(ic)) during osmotic swelling. After 2 hr in 10 mOsm buffer, eggs remained intact, while 60.2 +/- 7.0% of oocytes had burst. Water uptake was proportional to buffer osmolarity in oocytes, but not in eggs. We did not see a regulatory volume decrease in the cells, nor was there any evidence for osmolyte efflux. Oocyte P(ic) increased from 0.27 cm H2O (range 0.14-0.61 cm H2O) to 5.92 cm H2O (range 2.52-7.18 cm H2O, P < 0.001) after 70 min in 20 mOsm buffer. Egg P(ic) in 20 mOsm buffer (0.04 cm H2O, range -0.07 to 0.014 cm H2O) was not significantly different from the value in isotonic (200 mOsm) buffer (0.14 cm H2O, range 0-0.16 cm H2O). The data indicate that Vc in oocytes and eggs is not regulated by either plasma membrane ion transport or the mechanical properties of the vitelline envelope. While oocytes appear to behave as passive osmometers, we speculate that the ability of eggs to maintain volume is determined, in part, by the cytoplasm, in particular by its gel-like nature.

Dissociation and unfolding of the pyruvate dehydrogenase complex by guanidinium chloride

The effect of guanidinium chloride (GdnHCl) on the pyruvate dehydrogenase complex (PDC) from bovine heart and its constituent enzymes has been studied. The overall activity of the complex is lost reversibly at low levels of GdnHCl (0.2 M) which cause 40-50% inactivation but no loss of overall secondary or tertiary structures of the individual enzymes; the inactivation of the complex is shown to be caused by dissociation of the E1 and E3 components from the E2/X core assembly. This provides an improved procedure for controlled dissociation of the complex and efficient recovery of its component enzymes in their native states. Higher concentrations of GdnHCl (up to 4 M) lead to the unfolding and irreversible inactivation of the separate enzymes of the complex with the E2/X core proving the most resistant to GdnHCl-induced unfolding. Neither the 60-meric E2/X core assembly nor the dimeric E3 component are dissociated into monomers in the presence of 6 M GdnHCl; the latter enzyme forms higher-M(r) aggregates under these conditions.

Probing the details of the HIV-1 Rev-Rev-responsive element interaction: effects of modified nucleotides on protein affinity and conformational changes during complex formation

The solution structure of the human immunodeficiency virus type 1 (HIV-1) Rev-responsive element (RRE) has been investigated by enzymic and chemical structural probing of a 71 nt RRE transcript. The minimum sequence information required to maintain recognition by the Rev protein has previously been mapped to a 29 nt stem-loop structure, known as minSLIIB. The key recognition target is a single-stranded RNA bubble at the base of the RNA stem. The fine details of RNA recognition have been probed using chemically synthesized minSLIIBs containing variant base or sugar residues at sites within the bubble. These have been analysed by gel retardation assays and their relative affinities for Rev protein determined. Complex formation between the wild-type minSLIIB RRE and Rev protein was also monitored using CD spectroscopy, which suggests a change in RNA conformation upon Rev binding. The spectral change is consistent with localized melting of RNA, leading to a decrease in the level of base stacking and/or a change in base tilting, during formation of the complex. Deoxynucleotide substitutions on just one side, the 5' side, of the bubble inhibit the conformational change detected by CD. The data are consistent with a dynamic interaction between Rev and its target site. The contact points between Rev and the RRE were probed directly using photo-cross-linking with either ribo-5-bromouridine- or ribo-4-thiouridine-substituted minSLIIBs. The data are consistent with protein-RNA contacts at the bottom of the bubble.

The ABA-1 allergen of the parasitic nematode Ascaris suum: fatty acid and retinoid binding function and structural characterization

We report here on the structure and function of the ABA-1 allergen protein of the parasitic nematode Ascaris, the first nematode allergen to be characterized in detail. Using the fluorescent fatty acid analog 11-(((5-(dimethylamino)-1-naphthalenyl)sulfonyl)amino)undecanoic acid (DAUDA), it was demonstrated that ABA-1 is a fatty acid binding protein (FABP) with a high affinity for the fluorescent analog (8.8 x 10(-8) M) and for oleic acid in competition experiments (1.3 x 10(-8) M), with a single binding site for ligand per monomer unit. Blue-shifting of fluorescence emission of DAUDA upon binding was unprecedented in degree among FABPs, being equivalent to that occurring in cyclohexane. A similarly blue-shifted spectrum was obtained with a probe in which the fluorophore was bound to the alpha carbon of a fatty acid, indicating that the carboxylate group of bound fatty acids is probably not exposed to solvent. In competition experiments and by observation of changes in their intrinsic fluorescence, retinol and retinoic acid were also found to bind in the fatty acid binding site. Circular dichroism (CD) of the ABA-1 protein revealed a high alpha-helix content (59%) which was consistent with the four-helix structure for the protein predicted from sequence algorithms. Fluorescence measurements showed that the single, highly conserved tryptophan residue is deeply buried in an unusually apolar environment and that this was unaffected by ligand binding. DSC studies of thermal stability indicate that unfolding of the ABA-1 dimer is cooperative and biphasic (Tm approximately 71 and 89 degrees C), suggesting a two-domain thermal unfolding process, again consistent with the predicted structure. Only the folding of the high-temperature domain is reversible on cooling. DSC confirmed the gel filtration analysis, which indicated that ABA-1 forms a dimer. Aside from being the first nematode allergen for which structure or function has been elucidated, ABA-1 provides a highly manipulable model for investigation of the interaction between hydrophobic ligands and alpha-helical proteins.

Detection of Salmonella typhimurium from rectal swabs of experimentally infected beagles by short cultivation and PCR-hybridization

A rapid and sensitive cultivation and PCR-hybridization procedure for the detection and identification of Salmonella typhimurium was evaluated over a 42-day period with eight experimentally infected beagles. Rectal swabs were taken at several times postinfection, inoculated into selenite-cystine broth, and plated onto Hektoen-Enteric Enteric agar immediately after incubation for 4 and 24 h. PCRs and hybridizations were also conducted with each sample, and the results were compared with those of standard culture techniques to evaluate the efficiency of the PCR-hybridization procedure. The PCR-hybridization procedure was more sensitive than standard culture techniques at each enrichment incubation (P < 0.05). In addition, the PCR-hybridization procedure was significantly better than culture up through 3 days postinfection (P < 0.05). A nonspecific amplified product, relatively close in size to the 457-bp specifically amplified product, did not hybridize to an internal oligonucleotide probe or to a random-primed labeled probe. Subsequent sequence information revealed that the product had very little similarity to the 457-bp product but had significant similarity to an Escherichia coli aldehyde dehydrogenase gene. This study indicated that a cultivation and PCR-hybridization procedure is significantly better than culture for the identification of S. typhimurium. Additionally, the results confirm the importance of determining specificities of PCR products beyond the gel electrophoresis level by hybridization with a specific probe.

Purification and characterization of the periplasmic nickel-binding protein NikA of Escherichia coli K12

The nik operon of Escherichia coli encodes a periplasmic binding-protein-dependent transport system specific for nickel. In this report, we describe the overproduction of the periplasmic nickel-binding protein NikA by cloning the nikA gene into an overexpression vector, pRE1. NikA was purified free of nickel to near homogeneity from the periplasm by hydrophobic and ion-exchange chromatography. N-terminal amino acid sequencing confirmed that the leader peptide of NikA had been removed. The nickel-binding properties of the protein has been studied by monitoring the quenching of intrinsic protein fluorescence. NikA binds one atom of nickel/molecule of protein with a dissociation constant (Kd) of less than 0.1 microM. Other metals (cobalt, copper, iron) are bound at least 10-fold less tightly. The high specificity for Ni2+ is also demonstrated by high-performance immobilized-metal-ion affinity chromatography. Biosynthesis of NikA occurred only under anaerobic conditions and was dependent on the general anaerobic regulator FNR. It was repressed by the presence of 250 microM Ni2+ in the growth medium and was not affected by either 30 mM formate or 100 mM nitrate. Anaerobically grown wild-type strain MC4100 contains about 23,000 molecules of NikA/cell. In addition to the effect on nickel transport, nikA mutation affects also the nickel sensing in Tar-dependent repellent chemotaxis.

The Bateman bipolar prosthesis: a prospective study in primary osteoarthritis

We present a prospective study of Bateman bipolar prosthesis performed over 5 years in Perth. All patients were treated for primary osteoarthritis using a cementless straight Moore stem and the bipolar acetabular component. Assessment was made at 6-monthly intervals. Harris hip scores were calculated and radiological parameters of inner bearing movement, component migration and proximal osteoporosis were assessed. The group comprised 76 prostheses in 72 patients. The mean Harris hip score at 3 years follow-up was 85, however with a wide range between 55 and 99. A total of 30% of patients at 3 years follow-up had a Harris hip score at less than 70. Twenty-seven per cent of the prostheses at 3 years had restriction of movement at the inner bearing and 43% were judged to have moderate or severe stress shielding around the proximal femur. The clinical results were unpredictable with thigh pain being a significant problem. Because of the unpredictable results we would not advocate the use of the Bateman prosthesis in primary osteoarthritis.