PubMed Health⌕ Search

Biomedical subjects

D J Walker

Publications and source records attributed to D J Walker.

At least 19 recordsLinked to original sources
PubMed1998

The Plasmodium falciparum translationally controlled tumor protein homolog and its reaction with the antimalarial drug artemisinin.

Artemisinin and its derivatives are important new antimalarial drugs. When Plasmodium falciparum-infected erythrocytes are incubated with [10-3H]dihydroartemisinin, several malaria-specific proteins become labeled. One of these proteins is the P. falciparum translationally controlled tumor protein (TCTP) homolog. In vitro, dihydroartemisinin reacts covalently with recombinant TCTP in the presence of hemin. The association between drug and protein increases with increasing drug concentration, plateauing at approximately 1 drug/TCTP molecule. By Scatchard analysis, there appear to be 2 hemin binding sites on TCTP with dissociation constants of approximately 18 microM. When the single cysteine moiety is blocked by pretreatment with iodoacetamide, hemin binding is not affected, whereas drug binding is reduced by two-thirds. Thus, TCTP reacts with artemisinin in situ and in vitro in the presence of hemin and appears to bind to hemin. The function of the malarial TCTP and the role of this reaction in the mechanism of action of artemisinin await elucidation.

Amino Acid Sequence↗
PubMed1998

Developmental and tissue-specific expression of 2-methyl branched-chain enoyl CoA reductase isoforms in the parasitic nematode, Ascaris suum.

The 2-methyl branched-chain enoyl CoA reductase (ECR) plays a pivotal role in the reversal of beta-oxidation operating in anaerobic mitochondria of the parasitic nematode, Ascaris suum. Two-dimensional gel electrophoresis of the purified ECR yielded multiple spots, with two distinct but overlapping N-terminal sequences. These multiple isoforms were not the result of population effects, as the pattern observed on 2-D gels of the purified ECR was identical to those on immunoblots of muscle homogenates isolated from individual worms. A full-length cDNA coding for the major ECR isoform (ECRI) has been cloned and sequenced and compared with that of the minor isoform (ECRII) which has been described previously (Duran et al. J Biol Chem 1993;268:22391-22396). ECRI contained the 22-nucleotide trans-spliced leader sequence characteristic of many nematode mRNAs, a 5' untranslated region (UTR) of 13 nucleotides, an open reading frame (ORF) of 1257 nucleotides, a 3'-UTR of 110 nucleotides that included the polyadenylation signal AATAAA downstream of the termination codon and a short poly(A) tail. The ORF predicted a 16 amino acid leader sequence not found in the native protein and a mature protein of 403 amino acids with a molecular weight of 43 698 and a predicted pI of 6.2. ECRI and ECRII were 73% identical at the predicted amino acid level and their mRNAs exhibited significant structural similarity even though they were products of separate genes. Comparison of ECRI and ECRII with the sequences of acyl CoA dehydrogenases from a variety of different sources revealed a high degree of interspecies sequence identity, suggesting that these enzymes may have evolved from a common ancestral gene. This result is surprising since the ascarid enzymes function as reductases, not as dehydrogenases. Both ECRs were tissue-specific and developmentally regulated and were found in transitional third-stage larvae (L3) and adult muscle, but not in early, aerobic larval stages or adult testis, ovary, or intestine. The ratio of ECRII to ECRI was greater in L3 than in adult muscle. Interestingly, both ECRs also appeared to be expressed in pharyngeal muscle, suggesting that branched-chain fatty acid synthesis may not be confined exclusively to body wall muscle.

Amino Acid Sequence↗
PubMed1998

Ambulatory activity as an objective and quantifiable measure of nonsteroidal therapy.

OBJECTIVE: To quantify any increase in short term spontaneous ambulatory activity resulting from the use of nonsteroidal antiinflammatory drugs (NSAID) in patients with rheumatoid arthritis (RA). METHODS: Double blind placebo controlled crossover study of 8 women with RA using conventional assessments and the Numact activity monitor. RESULTS: Patients' ambulatory activity was 50% greater during NSAID treatment compared to placebo treatment. Effect size calculated at 0.62, suggesting good sensitivity to change. The increased activity occurred late morning. CONCLUSION: Spontaneous ambulatory activity is an objective and relevant measure of disability.

Adult↗
PubMed1997

Hymenolepis diminuta: mitochondrial NADH --> NAD transhydrogenation and the lipoamide dehydrogenase system.

The occurrence of NADH --> NAD transhydrogenation and lipoamide dehydrogenase activities was demonstrated for cysticercoids of the intestinal cestode, Hymenolepis diminuta. In addition, both activities were catalyzed by the mitochondria of 6-, 10-, and 14-day H. diminuta and by the mitochondria from immature, mature, and pregravid/gravid regions of the adult cestode. A developmentally related increase in NADH --> NAD activity was suggested and the levels of both activities in the immature region of the helminth were consistent with it being a region of high metabolic activity. Adult H. diminuta mitochondrial lipoamide dehydrogenase was purified to homogeneity. The native enzyme was a homodimer with a monomeric and dimeric molecular mass of 47 and 93 kDa, respectively. Spectral analyses revealed that the enzyme contained flavin. More importantly, the purified enzyme catalyzed appreciable NADH --> NAD transhydrogenation activity, a premier finding for the phylum Platyhelminthes. The ratio of NADH --> NAD transhydrogenation to lipoamide reduction was 1:5. Both activities were inhibited by Cu2+ and Cd2+ with the NADH --> NAD activity being more resistant to inhibition. Interestingly, aside from NADH diaphorase activity, the cestode enzyme displayed NADH-ferricyanide reductase and, to a lesser degree, NADPH --> NAD transhydrogenation activities. The partial amino acid sequence of H. diminuta lipoamide dehydrogenase indicated that this enzyme was most similar to the corresponding enzymes of other parasitic helminths. Moreover, the phenylalanine for leucine substitution found in the redox-active disulfide site of the lipoamide dehydrogenases of some anaerobic systems was noted for the H. diminuta enzyme.

Amino Acid Sequence↗
PubMed1997

Establishment of human tubal epithelial cells for coculture in an IVF program.

OBJECTIVE: Our goal was to develop a coculture system from human tubal epithelial cells for use in a human IVF program. DESIGN: Fallopian tubes were obtained from women undergoing hysterectomy for benign disease. Ampullary epithelial cells were cultured, passaged, and frozen and the karyotype and epithelial characteristics of later passages examined. SETTING: The study took place at the Assisted Conception Clinic, Walsgrave Hospital, and the Department of Biological Sciences, University of Warwick. RESULTS: Ampullary epithelial cells can be successfully cultured and maintained as diploid epitheliod lines until the fifth passage. Freezing does not affect subsequent culture, the cytoskeleton, or the karyotype. In excess of 12 x 10(6) cells may be obtained from a pair of Fallopian tubes. CONCLUSIONS: The ease of establishing and maintaining human tubal epithelial cell cultures justified their use in clinical IVF for human embryo cocultures, and further investigations into their mode of action should be encouraged.

Cells, Cultured↗
PubMed1997

A continuous patient activity monitor: validation and relation to disability.

The measurement of patient activity over prolonged periods has been attempted with accelerometer-based devices, but these summate total acceleration and deceleration over time periods, are difficult to relate to recognizable activities and are influenced by passive movement. We describe the development of a portable monitor of ambulation. This logs posture (sitting, standing and lying) and number and vigour of steps in real time over prolonged periods, usually 24 h. This is based on a system of position sensors and an accelerometer which is sampled when the subject is standing. Data are processed through an interface and stored on a Psion Series 3 'palm top' computer. The system has been validated against observation, and the relationship of activity to disability in rheumatoid arthritis explored.

Adult↗
PubMed1997

Compound heterozygosity for the shared epitope and the risk and severity of rheumatoid arthritis in extended pedigrees.

The objective was to explore the role of HLA-DRB1 genes in determining disease severity in rheumatoid arthritis (RA). The population comprised extended pedigrees of 17 multicase RA families. Family members were genotyped for both HLA-DRB1 alleles using restriction fragment length polymorphism (RFLP). Identification of HLA-DRB1*04 variants was performed using the Multiplex ARMS-RFLP technique. Compound heterozygote individuals carrying two different alleles containing the shared epitope (SE) were at greatest risk of developing RA (odds ratio = 36, 95% CI 9.1-143). A synergistic or additive effect of these alleles is suggested. Individuals carrying no SE alleles expressed milder disease, as measured by the Spread Severity (SS) index, compared to compound heterozygotes (P = 0.045). Compound heterozygosity was not invariably associated with severe disease with six (50%) having clinically mild disease at a median age of 57.5 yr and median disease duration of 16 yr. Inheriting two different SE-bearing alleles results in an increased risk of RA and, on average, greater disease severity. This is not, however, invariably associated with severe disease, making it of limited use as a predictor of prognosis.

Adult↗
PubMed1996

Identification of a novel dihydrolipoyl dehydrogenase-binding protein in the pyruvate dehydrogenase complex of the anaerobic parasitic nematode, Ascaris suum.

A novel dihydrolipoyl dehydrogenase-binding protein (E3BP) which lacks an amino-terminal lipoyl domain, p45, has been identified in the pyruvate dehydrogenase complex (PDC) of the adult parasitic nematode, Ascaris suum. Sequence at the amino terminus of p45 exhibited significant similarity with internal E3-binding domains of dihydrolipoyl transacetylase (E2) and E3BP. Dissociation and resolution of a pyruvate dehydrogenase-depleted adult A. suum PDC in guanidine hydrochloride resulted in two E3-depleted E2 core preparations which were either enriched or substantially depleted of p45. Following reconstitution, the p45-enriched E2 core exhibited enhanced E3 binding, whereas, the p45-depleted E2 core exhibited dramatically reduced E3 binding. Reconstitution of either the bovine kidney or A. suum PDCs with the A. suum E3 suggested that the ascarid E3 was more sensitive to NADH inhibition when bound to the bovine kidney core. The expression of p45 was developmentally regulated and p45 was most abundant in anaerobic muscle. In contrast, E3s isolated from anaerobic muscle or aerobic second-stage larvae were identical. These results suggest that during the transition to anaerobic metabolism, E3 remains unchanged, but it appears that a novel E3BP, p45, is expressed which may help to maintain the activity of the PDC in the face of the elevated intramitochondrial NADH/NAD+ ratios associated with anaerobiosis.

Amino Acid Sequence↗
PubMed1996

Improving the efficiency and cost-effectiveness of food aid grain delivery.

Grain food aid averages 13 million tons per year. Donors have a duty to deliver food aid grain in an adequate and acceptable condition at least cost. This paper reviews commodity procurement, packaging, inspection, shipping and storage with regard to overall quality assurance and cost-effectiveness. Experience at ports of loading and discharge and in food aid delivery programmes indicates that sufficient attention is rarely paid to quality assurance and loss minimisation. Grain procurement specifications that are normally appropriate for safe handling and storage in temperate climates, particularly moisture content, are commonly inappropriate for tropical climates. The technology for safe delivery of food aid grain is well established but not always implemented. Procurement of food aid grain in developing countries has increased recently, creating a need to improve operational and management aspects of tendering and quality assurance procedures. Such purchases entail potential cost savings but are associated with lengthening delivery lead times for non-urgent consignments. Although woven polypropylene sacks are cheaper to buy than jute ones, the losses associated with handling and storage problems indicate that jute sacks are preferable for food aid delivery.

Cost-Benefit Analysis↗
PubMed1996

Effects of cocaine on briefly signaled versus completely signaled delays to reinforcement.

Key pecking by 4 pigeons was maintained by a multiple schedule consisting of two variable-interval 60-s schedules wherein each food presentation followed a nonresetting 27-s delay that was either briefly signaled at its outset or completely signaled. Brief-signal duration was adjusted so that response rates maintained by the briefly and completely signaled delays of reinforcement were similar. In general, acute administration of small to intermediate doses (0.3 to 3.0 mg/kg) of cocaine produced either small increases in response rates in both components or no change, and larger doses (5.6 to 13.0 mg/kg) decreased response rates. Chronic (i.e., daily) cocaine administration (10.0 mg/kg) resulted in tolerance to the rate-decreasing effects in both components. Cocaine's effects were generally similar whether delays were completely or briefly signaled. Discontinuation of cocaine administration and subsequent removal of the delay signals also had similar effects in both components of the multiple schedule. Taken together, these results are consistent with the view that the two types of delay signals were equally effective in maintaining responding during the variable-interval schedules.

Animals↗
PubMed1995

Mitochondrial NADH-->NAD transhydrogenation in adult Hymenolepis diminuta.

Adult Hymenolepis diminuta mitochondria catalyze a transhydrogenation reaction between NADPH and NAD and between NADH and NAD. The NADPH-->NAD reaction is catalyzed by an inner membrane-associated pyridine nucleotide transhydrogenase, whereas the NADH-->NAD reaction is ostensibly catalyzed by another system(s). The source(s) of NADH-->NAD activity was evaluated by assessments of its intramitochondrial distribution and thermal lability and by comparisons with the distribution/thermal lability of NADH dehydrogenase, lipoamide dehydrogenase, and NADPH-->NAD transhydrogenase. The occurrence of NADH and lipoamide dehydrogenase components was readily demonstrable. Like NADPH-->NAD transhydrogenase, NADH dehydrogenase was essentially membrane bound. Lipoamide dehydrogenase and NADH-->NAD activities were, at different levels, in the membrane and soluble fractions. Based on thermal profiles, NADH and lipoamide dehydrogenase differed from each other and from NADPH-->NAD transhydrogenase. Although the NADH-->NAD profile closely paralleled that for lipoamide dehydrogenase, it also was similar to the NADH dehydrogenase profile. Collectively, these data are consistent with the supposition that the H. diminuta mitochondrial NADH-->NAD transhydrogenation reaction is catalyzed by lipoamide dehydrogenase and possibly by NADH dehydrogenase rather than by an independent transhydrogenase system.

Animals↗
PubMed1994

Anti-Proteus antibodies and Proteus organisms in rheumatoid arthritis: a clinical study.

We have studied anti-Proteus antibodies (APA), isolation of Proteus, and their relation to various measures of RA disease activity. Seventy RA patients with a CRP > 10 mg/l had higher APA titres than 17 RA patients with CRP < or = 10 mg/l (P = 0.006), and 36 non-RA controls (P = 0.003). However, in a cross-sectional study of the RA group, there was no correlation between APA and a number of clinical and laboratory measures of disease activity, including the CRP and Stoke RA activity index. A longitudinal study showed no correlation between changes in these measures of disease activity and change in APA titre. We were unable to isolate Proteus in the urine or faeces of RA patients more frequently than controls, and the isolation of Proteus did not correlate with serum APA titres. Urinary APA was present in equal frequencies in RA and non-RA patients. NSAIDs, DMARDs and steroids did not appear to influence APA titres in the RA group. These results suggest that APA may act as an acute phase protein, distinct from CRP, but not correlating with RA disease activity in its broadest context. The fact that the antibody we are measuring binds to Proteus may be irrelevant, and the study does not support a role for Proteus in RA.

Adult↗
PubMed1994

Six-year follow-up of multiple joint replacement surgery to the lower limbs.

We report a 6-yr follow-up study of an original population of 50 patients who had three or more major joints (hips and knees) replaced. Thirty-one of 32 surviving patients were still ambulant in the community, and all patients described significant pain relief. No RA patient was requiring permanent inpatient or residential care and the family remained the main social support. They remained a very disabled group with a median Health Assessment Questionnaire score of 2.75. Ten required revision surgery: three hips and seven knees; four patients required their fourth lower limb joint (hip/knee) replaced and seven patients required surgery to the upper limbs and nine feet during the follow-up period. The median 10-yr survival of hip and knee arthroplasties in multiple joint replacement (MJR) patients with RA was 90.5 and 78.6% respectively. There was an increased incidence of cervical myelopathy in MJR patients 16.9%. The mortality rate was higher than expected (standardized mortality ratio = 590) but the actual surgery was not implicated. MJR therefore appears to be a worthwhile policy, even at long-term follow-up.

Arthritis, Rheumatoid↗