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A Edwards

Publications and source records attributed to A Edwards.

At least 127 records · Page 7Linked to original sources
PubMed1996

Evidence that a 77-kilodalton protein from the starch of pea embryos is an isoform of starch synthase that is both soluble and granule bound.

In this paper we provide further evidence about the nature of a 77-kD starch synthase (SSII) that is both soluble and bound to the starch granules in developing pea (Pisum sativum L.) embryos. Mature SSII gives rise to starch synthase activity when expressed in a strain of Escherichia coli lacking glycogen synthase. In transgenic potatoes (Solanum tuberosum L.) expressing SSII, the protein is both soluble and bound to the starch granules. These results confirm that SSII is a starch synthase and indicate that partitioning between the soluble and granule-bound fraction of storage organs is an intrinsic property of the protein. A 60-kD isoform of starch synthase found both in the soluble and granule-bound fraction of the pea embryos is probably derived by the processing of SSII and is a different gene product from GBSSI, the exclusively granule-bound 59-kD isoform of starch synthase that is similar to starch synthases encoded by the waxy genes of cereals and the amf gene of potatoes. Consistent with this, expression in E. coli of an N-terminally truncated version of SSII gives rise to starch synthase activity.

Amino Acid Sequence↗
PubMed1996

Identification of the major starch synthase in the soluble fraction of potato tubers.

The major isoform of starch synthase from the soluble fraction of developing potato tubers has been purified and used to prepare an antibody and isolate a cDNA. The protein is 140 kD, and it is distinctly different in predicted primary amino acid sequence from other isoforms of the enzyme thus far described. Immunoinhibition and immunoblotting experiments and analysis of tubers in which activity of the isoform was reduced through expression of antisense mRNA revealed that the isoform accounts for approximately 80% of the activity in the soluble fraction of the tuber and that it is also bound to starch granules. Severe reductions in activity had no discernible effect on starch content or amylose-to-amylopectin ratio of starch in tubers. However, they caused a profound change in the morphology of starch granules, indicative of important underlying changes in the structure of starch polymers within the granule.

Amino Acid Sequence↗
PubMed1996

Molecular scanning of candidate mitochondrial tRNA genes in type 2 (non-insulin dependent) diabetes mellitus.

Mitochondrial DNA (mtDNA) gene defects may play a role in the development of non-insulin dependent diabetes mellitus (NIDDM). In order to search for potentially diabetogenic mtDNA defects we have applied the technique of single stranded conformational polymorphism (SSCP) analysis to 124 patients with a history of NIDDM and 40 non-diabetic controls. No new heteroplasmic mutations were detected. However, a variety of homoplasmic variants were found in patients with NIDDM; some of these merit further investigation.

Base Sequence↗
PubMed1996

Resistance to biodegradative stress cracking in microporous vascular access grafts.

Degradative cracking, more commonly known as "environmental stress cracking" (ESC) has been observed in many implanted polyetherurethane elastomers. This phenomenon has been attributed to biochemical and cellular interactions at the surface of the implanted material causing polymer chain cleavage. This may result in surface fissuring followed by the deep cracking associated with considerable biodegradation of the polymer, resulting in loss of mechanical strength and the formation of aneurysms in an in vivo situation. These cracking effects are believed to be due to mechanical stress combined with the oxidising actions of macrophages and giant cells, as surface cracking has been observed to occur directly under adherent macrophages on a polyetherurethane implant. These cells form part of the body's immune response which uses enzymes and reactive oxygen species (O2, O2-, and HO. and H2O2) to degrade foreign material. We describe a modification of an in vitro test method developed by Zaho et al. [1] using glass wool and a Hydrogen Peroxide/Cobalt (II) Chloride (H2O2/CoCl2) mixture to replicate the oxidising effects of macrophages in vivo. The modifications were made to establish a routine testing system for resistance to biodegradation which could be used to screen a range of polymers designed for use in microporous vascular grafts. The grafts are pre-stressed by a method devised by Stokes et al. [2] where each graft is stretched to a predetermined elongation over a mandrel and the strain is fixed by tying PTFE tape around each end of the mandrel.

Biocompatible Materials↗
PubMed1995

Immunogenic HIV variant peptides that bind to HLA-B8 can fail to stimulate cytotoxic T lymphocyte responses.

Cytotoxic T lymphocyte responses in HIV infection can be impaired through variation in the epitope regions of viral proteins such as a gag. We report here an analysis of variant epitope peptides in three gag epitopes presented by HLA B8. Fifteen variant peptides were examined for their binding to HLA-B8; all but one bound at concentrations comparable to known epitopes. All except two of those that bound could be recognized by CTL from an HLA-B8 positive HIV-1-infected patient and were therefore immunogenic. However, in a hemophiliac patient studied in detail, there was a failure to respond to two immunogenic peptide epitopes representing virus present as provirus in the patient's peripheral blood. In one case, the patient's CTL had previously responded to the peptide; in the other case, there was a good response to a peptide of closely related sequence. Thus there was a selective failure of the CTL response to some proviral epitopes. This impaired reaction to new variants could contribute to the loss of immune control of the infection.

Animals↗
PubMed1995

Biochemical and molecular characterization of a novel starch synthase from potato tubers.

An isoform of starch synthase from potato tubers which is present both in the stroma of the plastid and tightly bound to starch granules has been identified biochemically and a cDNA has been isolated. The protein encoded by the cDNA is 79.9 kDa and has a putative transit peptide and a distinct N-terminal domain which is predicted to be highly flexible. It is similar in both amino acid sequence and predicted structure to the granule-bound starch synthase II (GBSSII) of pea embryos. When expressed in Escherichia coli, the mature protein has starch synthase activity. The importance of the isoform has been assessed by biochemical measurements and antisense transformation experiments in which the amount of the isoform in the tuber is severely and specifically reduced. Both approaches indicate that the isoform contributes a maximum of 15% of the total starch synthase activity of the tuber. It is suggested that this isoform and the GBSSII of pea embryos represent a widely distributed class of isoforms of starch synthase. The contribution to total starch synthase activity of members of this class probably varies considerably from one type of storage organ to another.

Amino Acid Sequence↗
PubMed1995

Error propagation in the estimation of glomerular pressure from macromolecule sieving data.

The theoretical effects of the glomerular transmural hydraulic pressure difference (delta P) on the sieving coefficients (theta i) of macromolecules of varying size have led to a number of attempts to use sieving curves to estimate delta P noninvasively, with inconsistent results. The objective of this study was to determine the extent to which experimental errors and imperfections in the theoretical models limit the ability to obtain reliable estimates of delta P using this method. Our approach was to generate many sets of synthetic "experimental data" using computer simulations of glomerular sieving and to compute values of delta P by fitting models to those data in the presence of various types and magnitudes of errors. Unbiased experimental errors were simulated by adding random amounts to individual values of theta i, and systematic errors were investigated by using a model based on one type of pore-size distribution to fit "data" generated using a model of a different type. We found that with random errors in theta i only, the estimate of delta P was accurate to within +/- 4 mmHg nearly all of the time, provided that the standard deviation, sigma i, was < or = 5% of theta i. When there were also systematic errors arising from the use of an "incorrect" form of pore-size distribution, a useful predictor of success was the probability P that the residuals, the differences between the measured and predicted sieving coefficients, were randomly distributed. A value of P > 0.2, as calculated from the algebraic signs of the residuals, indicated a high likelihood that the pressure estimate was accurate, provided that the random errors were sufficiently small. When P > 0.2, the fitted value of delta P was within +/- 4 mmHg of the true value in about 90%, 80%, and 70% of the cases examined when sigma i was < or = 2%, 5%, or 10% of theta i, respectively. An analysis of published data from a number of experimental studies indicated, however, that the favorable conditions of small sigma i and large P are extremely difficult to achieve, making it unlikely that an accurate group-mean value of delta P will be estimated from any given set of sieving data. Significant experimental and theoretical advances will be needed to make this a reliable method for estimating glomerular pressure.

Animals↗
PubMed1995

Development of a microporous compliant small bore vascular graft.

PURPOSE: To produce biodurable small diameter microporous vascular grafts with self-sealing properties for vascular access, for peripheral vascular and potentially for coronary artery bypass. The prosthesis should retain compliance and pulsatile flow in situ using a unique modus operandi permitting wall compression which accommodates changes in volume. METHOD: We have utilized efficient low temperature coagulation technology to develop a unique range of small diameter microporous vascular grafts using ChronoFlex, a biodurable polycarbonate urethane. RESULTS: Grafts have been subjected to a range of in vitro and in vivo testing, demonstrating excellent physical and mechanical characteristics, self-sealing, maintenance of compliance and pulsatile flow in situ and patency up to twenty-two weeks.

Animals↗
PubMed1995

The effect of low dose recombinant human growth hormone replacement on regional fat distribution, insulin sensitivity, and cardiovascular risk factors in hypopituitary adults.

GH deficiency is associated with increased cardiovascular morbidity, which may be determined by alterations in vascular risk factors. We report the effect of partially treated hypopituitarism and subsequent GH replacement (mean dose, 0.2 IU/kg.week) on putative cardiovascular risk factors in 22 nondiabetic hypopituitary subjects in a 6-month, double blind, controlled study (active/placebo ratio, 11:11). All patients were subsequently treated with GH for a further 6 months. Total fat, percent body fat, and central fat were measured by dual energy x-ray absorptiometry. The hypopituitary patients had increased percent fat (P = 0.03) and central fat (P < 0.01) compared with body mass index-matched controls. Before GH treatment, fasting (total) and specific insulin positively correlated with body mass index (P = 0.02 and P < 0.001, respectively), waist/hip ratio (P = 0.05 and P = 0.01), and central fat (P = 0.03 and P = 0.003). Specific insulin and insulin sensitivity (IS), calculated by homeostatic model of assessment, were related to total fat (P < 0.001 and P = 0.02). GH treatment for 6 months led to a reduction in total fat (P < 0.02), percent fat (P = 0.002), central fat (P = 0.012), waist/hip ratio (P < 0.05), total cholesterol (P = 0.03), and apolipoprotein-B (P = 00001), as well as a decrease in the IS from 36.9% (range, 12-100%) to 25% (range, 2.5-55%; P = 0.0002). This was paralleled by a rise in fasting (total) and specific insulin (P = 0.016 and P = 0.002). The degree of correlation among indices of IS, body composition, and fat distribution increased after GH treatment. Fasting plasma glucose rose significantly, but was within the reference range. During 12 months of GH therapy, a significant increase in serum lipoprotein-(a) was observed (P < 0.05). Although GH has beneficial effects on central adiposity and lipid fractions, it is also associated with a decrease in IS; these effects may vary between individuals.

Adipose Tissue↗
PubMed1994

Cytotoxic T-cell activity antagonized by naturally occurring HIV-1 Gag variants.

Most asymptomatic individuals infected with HIV-1 have a cytotoxic T lymphocyte (CTL) response to the virus Gag proteins which can be demonstrated in vitro. Epitopes have been mapped in p17 Gag and p24 Gag restricted by HLA-B8 (p17-3 and p24-13) and -B27 (p24-14). Viruses isolated from patients who make CTL responses to these peptides vary within the genetic sequences encoding these epitopes and some mutations lead to reduction in killing activity in vitro. This was attributed to either failure of the variant epitope to bind major histocompatibility complex class I or failure of T-cell receptors to bind the presented peptide. But peptide variants of class I-restricted epitopes cause 'antagonism', that is, the presence of a variant epitope (in the form of peptide) inhibits normal lysis of targets presenting the original epitope. This mirrors similar findings in class II-restricted systems. Here we report that naturally occurring variant forms of p17-3, p24-13 and p24-14 may cause antagonism of CTL lines derived from the same individuals. The effect is present if the epitopes are derived from synthetic peptides and when they are processed from full-length proteins expressed by either recombinant vaccinia constructs or replicating HIV.

Amino Acid Sequence↗
PubMed1994

Transvaginal embryo transfer during the zygote intrafallopian tube transfer procedure.

OBJECTIVE: Our purpose was to evaluate a tactile non-ultrasonographically directed approach to transvaginal tubal cannulation and embryo transfer during the zygote intrafallopian tube transfer procedure. STUDY DESIGN: We studied the application of the tactile approach to transvaginal tubal cannulation and embryo transfer in 68 consecutive zygote intrafallopian tube transfer cycles. RESULTS: The tactile approach to transvaginal tubal cannulation and subsequent embryo transfer was successful in 93% of couples. Pregnancy occurred in 16 of the 63 (25%) women undergoing a successful transvaginal embryo transfer. CONCLUSION: The tactile approach to transvaginal tubal cannulation was found to be easily learned and provided a safe and convenient method of tubal embryo transfer. This low-cost approach, which has application to transfer of both embryos and gametes, deserves further study.

Catheterization↗
PubMed1994

Heterosexual transmission of human immunodeficiency virus type 1 variants associated with zidovudine resistance.

During zidovudine therapy, human immunodeficiency virus type 1 (HIV-1) acquires a distinctive set of mutations that diminish the sensitivity of the virus to this drug in vitro. An AIDS patient is described who, while being treated with zidovudine, transmitted HIV-1 bearing a drug resistance mutation to a young woman who had never received zidovudine treatment. DNA sequencing of HIV-1 proviruses confirmed that these 2 persons shared HIV genetic variants, including a mutation at codon 70 in the reverse transcriptase gene associated with reduced in vitro sensitivity to zidovudine. This mutation persisted in the woman > 1 year in the absence of antiretroviral therapy. HIV-1 with genetic markers of zidovudine resistance can be transmitted heterosexually, but it is uncertain whether dissemination of drug-resistant virus will substantially reduce the usefulness of this drug.

Adult↗
PubMed1994

The autogenous latissimus breast reconstruction.

The autogenous latissimus flap is an alternative to tissue expansion and is the standard latissimus flap in reconstruction of the modified mastectomy defect. It is a useful autogenous reconstruction for partial mastectomy defects, and it serves as an alternative to the TRAM flap. The donor site is acceptable to patients, and the overall results are above average.

Back↗
PubMed1993

Large loop excision of the transformation zone (LLETZ) as an alternative to both local ablative and cone biopsy treatment: a series of 1000 patients.

One thousand patients, referred to the Oxford Colposcopy Clinic, were treated with either large loop excision of the transformation zone (LLETZ, 891 cases) or LLETZ cone (109 cases). Forty-five LLETZ cones were performed empirically, 64 under microcolposcopic guidance. Over 98% of patients were managed as outpatients under local anaesthesia, and 87% of new patients treated with LLETZ had treatment at their first visit. Ninety percent of patients had at least cervical intraepithelial neoplasia grade one (CIN I) and 73% had CIN II or worse. Seventeen cases of invasive or possibly invasive disease were detected, 6 of them unsuspected. The overall rate of complete excision of CIN or worse was 72%. Follow-up was cytologic with or without colposcopy depending on lesion severity. Ninety-one percent of 967 treated patients were free of dyskaryosis at a mean follow-up of 23 months, with complete excision of CIN or worse at LLETZ a significant predictive factor. No cases of invasive carcinoma have developed following treatment. Major morbidity was uncommon, with 3.8% severe hemorrhage. Stenosis was noted in 3.8% cases, mostly after LLETZ cone. One patient (0.1%) has reduced fertility possibly attributable to LLETZ. Questionnaire assessment revealed a very high degree of acceptability of the treatment to patients. LLETZ and LLETZ cone have proved highly acceptable and effective outpatient diagnostic and treatment alternatives to both local ablation and cone biopsy in the Oxford Colposcopy Clinic.

Adolescent↗