PubMed Health⌕ Search

Biomedical subjects

A P Turner

Publications and source records attributed to A P Turner.

16 recordsLinked to original sources
PubMed1992

Involvement of a neutral glycolipid in differential cell adhesion in the Xenopus blastula.

Many different molecular species mediate cell adhesion during embryonic development. These can have either protein or carbohydrate functional groups, which can act in either a homophilic or a heterophilic manner, and often in concert. We report here that a monoclonal antibody, M4B, raised against Xenopus blastomere membranes, inhibits the calcium-dependent adhesion of dissociated blastomeres. M4B maintains its inhibitory effect on adhesion when converted into univalent fragments, and specifically affects calcium-dependent adhesion. The antigen is regulated in both space and time during early development. It is found on cell surfaces throughout the egg to blastula stages, but is more concentrated on cells in the animal and marginal zones of the blastula. It is dramatically downregulated during gastrulation, and becomes largely restricted to gut epithelium by the larval stages. We show also that M4B function is spatially differentiated at the blastula stage, since it inhibits the aggregation of dissociated animal cells to a greater extent than vegetal cells. This membrane antigen may therefore play a role in the differential adhesion observed between different regions of the blastula, and which we presume to underlie the segregation of the primary germ layers during gastrulation. M4B recognizes a complex of plasma membrane glycolipids. Periodate treatment destroys the ability of these glycolipids to react with the antibody, indicating that the epitope resides in the carbohydrate moiety of the glycolipids. Chemical characterization shows that it is a neutral glycolipid, and that the major component is of the glycoglycerolipid, rather than the more common glycosphingolipid class. Blocking experiments with oligosaccharides of defined structure, and antibody crossreactivity show that the M4B antibody does not recognize several known embryonic carbohydrate antigens. These results demonstrate that M4B antibody recognizes a novel group of developmentally regulated glycolipids which function in calcium-dependent cell--cell adhesion in the Xenopus blastula.

Animals↗
PubMed1991

Biosensors for process control.

Biosensors have been extensively studied during the last 20 years, and a myriad of laboratory biosensors have been developed. Improvements are required in biosensor design and performance before they become widely accepted in industrial process monitoring. However, as the biotechnology industry expands, biosensors may become more acceptable because, despite their limitations, they are the only devices capable of delivering the information required.

Biosensing Techniques↗
PubMed1991

The design and development of new chemical sensors for in vivo monitoring.

The latest workshop of the European Community (EC) Concerted Action on 'Chemical sensors for in vivo monitoring' was held in Nauplion, Greece, in April this year. This fifth workshop focused on 'The design and development of new sensors for in vivo monitoring', and was organized into five sessions: design and development of new sensors; operational considerations; performance of analytical systems; novel sensors/tissue heterogeneity; and infra-red spectroscopy.

Biosensing Techniques↗
PubMed1989

Whole-cell biosensors for environmental monitoring.

Concern over the pollution risk to drinking water from industry and agriculture is growing, and the need for continuous on-line monitoring recognised. There is increasing use of living organisms as the sensitive agent to detect the presence of pollutants, and whole-cell biosensors are seen to have particular advantages in such environmental monitoring. The development of a mediated amperometric biosensor, incorporating the cyanobacterium Synechococcus as the biocatalyst, for on-line herbicide monitoring is described. The biosensor is able to detect a wide range of herbicides with sites of action on the photosynthetic electron transport chain, at concentrations down to 20 micrograms litre-1 and possesses a working life of up to 7 days. The use of alginate immobilisation of the biocatalyst to overcome the problems associated with obtaining a realistic shelf life for the biosensor is discussed.

Biosensing Techniques↗
PubMed1989

Rapid determination of the glucose content of molasses using a biosensor.

A knowledge of the sugar content of molasses is of commercial importance to a number of industrial fermentations. Hence the feasibility of using a glucose oxidase biosensor to determine the glucose content of molasses samples was investigated. This method was compared with standard high-performance liquid chromatographic (HPLC) and gas-liquid chromatographic (GLC) procedures and with the use of a commercially available glucose analyser. A good correlation was obtained between the standard acetic anhydride GLC and glucose oxidase biosensor results (correlation coefficient = 0.98). Rapid and accurate measurements could be carried out using the biosensor without the need to employ the sample preparation step required in standard GLC methods. It was concluded that the use of the biosensor technique for the determination of glucose in molasses samples has distinct advantages over conventional methods.

Biosensing Techniques↗
PubMed1989

Ferrocene modified polypyrrole with immobilised glucose oxidase and its application in amperometric glucose microbiosensors.

Gold microelectrodes were modified with electropolymerised polypyrrole in both organic and aqueous electrolytes. Cyclic voltammetry studies confirmed that electron conduction through the films in aqueous electrolytes is greatly reduced and is inefficient at mediating the oxidation/reduction of solution redox species. Films formed in aqueous electrolyte were also found to be more heterogenous in structure compared to those formed in acetonitrile. Aqueous polymerised films were used as an immobilisation matrix for glucose oxidase, and modified gold micro electrodes were used in the analysis of glucose using hydrogen peroxide detection. It was found that glucose oxidase was strongly absorbed into the films and that the sensors remained stable for several weeks. An improved linear range and oxygen insensitivity was achieved by incorporating the "water-insoluble" electron transfer mediator, dimethyl ferrocene, into the polypyrrole films by absorption. Good currents and response times to glucose addition were obtained from these electrodes, however, the electrodes possessed poor stability caused by the apparent loss of mediator from the films. Greater operational stability was achieved by covalently functionalising the films with the ferrocene derivative, ferrocenecarbonyl chloride. Covalently bound ferrocence was found to be an efficient oxidant of reduced glucose oxidase. Electrodes constructed in this manner possessed a good linear range, oxygen insensitivity and better stability. Electron transfer mechanisms are discussed.

Biosensing Techniques↗
PubMed1988

Amperometric enzyme-amplified immunoassays.

Enzyme-amplified immunoassays have been adapted for electrochemical measurement, using an NAD+/NADH redox cycle coupled to an electrode via the active site of diaphorase. Two amperometric methods are described, the first employs an organic conducting salt electrode, NMP+/TCNQ-; the second a platinum wire with ferricyanide as electron transfer mediator. In an immunoenzymometric assay for human prostatic acid phosphatase the sensitivities of the electrochemical methods were comparable to that achieved with the existing optical technique, but the dynamic range of the electrochemical assays was increased by at least two orders of magnitude. It is proposed that electrochemical enzyme-amplified immunoassays may eventually replace their optical counterparts.

Acid Phosphatase↗
PubMed1988

Optical and electrochemical detection of DNA.

There is a growing demand for the production of a DNA biosensor with applications in medicine, the food industry, agriculture, veterinary science and environmental science. In this paper we describe methods for the optical and electrochemical detection of DNA using the enzyme horseradish peroxidase (EC 1.11.1.7) and glucose oxidase (EC 1.1.3.4). We have used bis-methylacridinium nitrate and luminol for the optical detection of DNA using a purpose built, inexpensive luminometer. Using this system detection limits of 10(-11) g of plasmid DNA have been observed. Electrochemical detection of DNA was carried out by the use of a fluoride ion selective electrode and stripping voltammetry. DNA was detected down to 10(-9)-10(-10) g of DNA by the enzymatic release of halogen ions from organohalogen compounds.

Animals↗
PubMed1988

A glucose sensor utilising tetracyanoquinodimethane as a mediator.

This paper describes an amperometric enzyme electrode for glucose analysis. The electrode utilised the mediator tetracyanoquinodimethane (TCNQ) to facilitate electron transfer from glucose oxidase to a pyrolytic graphite carbon electrode. The electrode demonstrated a response to glucose in a clinically relevant range (0-70 mM). Results concerning the direct current cyclic voltammetry of TCNQ and the electrodes' response to glucose, pH profile and the effect of temperature are presented.

Biosensing Techniques↗