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Biomedical subjects

L D Stephens

Publications and source records attributed to L D Stephens.

18 recordsLinked to original sources
PubMed1995

An amperometric opiate assay.

Current techniques for the detection and measurement of diacetylmorphine (heroin), morphine and their principal metabolite morphine-3-glucuronide (M3G) are based mainly on chromatography or immunoassay. No enzymatic method for the detection of these compounds has yet been reported. Two novel microbial enzymes have been isolated and characterized in this laboratory: an acetylmorphine carboxyesterase (heroin esterase) and a morphine dehydrogenase (MDH). These highly specific enzymes have been incorporated in an amperometric assay for heroin and morphine using phenazine methosulphate as a mediator. The assay gives a rapid and sensitive response to heroin and morphine, with a detection limit for morphine of 6.8 micrograms ml-1 (23.7 microM).

Acetylesterase↗
PubMed1991

Microbial degradation of the morphine alkaloids. Purification and characterization of morphine dehydrogenase from Pseudomonas putida M10.

The NADP(+)-dependent morphine dehydrogenase that catalyses the oxidation of morphine to morphinone was detected in glucose-grown cells of Pseudomonas putida M10. A rapid and reliable purification procedure involving two consecutive affinity chromatography steps on immobilized dyes was developed for purifying the enzyme 1216-fold to electrophoretic homogeneity from P. putida M10. Morphine dehydrogenase was found to be a monomer of Mr 32,000 and highly specific with regard to substrates, oxidizing only the C-6 hydroxy group of morphine and codeine. The pH optimum of morphine dehydrogenase was 9.5, and at pH 6.5 in the presence of NADPH the enzyme catalyses the reduction of codeinone to codeine. The Km values for morphine and codeine were 0.46 mM and 0.044 mM respectively. The enzyme was inhibited by thiol-blocking reagents and the metal-complexing reagents 1,10-phenanthroline and 2,2'-dipyridyl, suggesting that a metal centre may be necessary for activity of the enzyme.

Alcohol Oxidoreductases↗
PubMed1990

Biosensors.

This review introduces biosensors as analytical devices that respond selectively to analytes in appropriate samples and convert their concentrations into electrical signals via a combination of a biological recognition system and a suitable transducer. The last decade has seen dramatic advances in the design of sensor configurations, the marriage of biological systems with modern monolithic silicon and optical technologies, the development of effective electron-exchange systems and the introduction of direct immunosensors.

Animals↗
PubMed1976

Joseph LeConte on evolution, education, and the structure of knowledge.

During the last quarter of the nineteenth century the theory of evolution profoundly influenced American thought. In the form of Social Darwinism it significantly shaped views on race, civilization, and political theory. Sociology and psychology were developing concurrently as disciplines. All of these were destined to have an effect upon education, for many intellectuals believed that science in general and evolutionary theory in particular were directly applicable to all areas of thought. Among the advocates of such a role for science and evolutionary theory was Joseph LeConte, whose views on the subject are outlined and compared with his contemporaries.

Art↗