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Biomedical subjects

J N Smith

Publications and source records attributed to J N Smith.

At least 37 records · Page 2Linked to original sources
PubMed1987

Seasonal changes in density and tissue distribution of Onchocerca cervicalis microfilariae in ponies and related changes in Culicoides variipennis populations in Louisiana.

Seasonal changes in density and spatial distribution of Onchocerca cervicalis microfilariae were studied in ventral-midline skin of 15 infected pony mares in southern Louisiana. Triple running mean analysis of data over a 13-mo period indicated that a distinct pattern exists in total microfilariae population density and in microfilariae occurrence in different levels of the dermis. Microfilariae density reaches peak levels in the spring followed by a 58% decrease in the summer, a 19% increase in the fall, and a decrease to the lowest numbers in the winter. Microfilariae were found in all levels of the skin during the spring, summer, and fall but were not found in the superficial layers of the dermis during the winter months. The population density of Culicoides variipennis, a demonstrated vector of O. cervicalis, appeared to have seasonal fluctuations similar to the changes in microfilarial density. Harmonic wave analysis of microfilariae density data in individual ponies showed that all individuals did not follow the population trend.

Animals↗
PubMed1984

Kinetic studies on a glutathione S-transferase from the larvae of Costelytra zealandica.

Of the glutathione S-transferases from the New Zealand grass grub (Costelytra zealandica) active in conjugating the model substrate 1-chloro-2,4-dinitrobenzene, the most active was isolated in a functionally homogeneous form. This had an isoelectric point of 8.7. Preliminary evidence suggests that it is a homodimer with subunits of Mr 23 500. The dependence of the enzyme-catalysed reaction on substrate concentration was analysed in terms of the rate equation characteristic of Ordered Bi Bi or Rapid-Equilibrium Random mechanisms. Evidence was found for a critical ionizing event at pH 9.3 at 37 degrees C. This event appears to involve a twofold change in charge on the enzyme, which may be the result of co-operative ionizations rather than independent ionizations. This appears to affect neither the binding of the aromatic substrate to the enzyme, nor the maximum catalytic velocity of the enzyme-catalysed reaction. The variation of the kinetics with temperature was studied. Apparent thermodynamic parameters characteristic of the reaction were derived. The possible relevance of the temperature-dependence of the enzyme-catalysed reaction in vivo is discussed.

Animals↗
PubMed1983

Acidic conjugate of phenols in insects; glucoside phosphate and glucoside sulphate derivatives.

Conjugates of p-nitrophenol in nine species of insects were identified by paper chromatography and ionophoresis as the glucoside, the sulphate, the phosphate and the glucoside phosphate. Metabolites with similar properties to the glucoside phosphates were also formed from 8-hydroxyquinoline, 1-naphthol and 4-methylumbelliferone in Tenebrio larvae. Tenebrio larvae also metabolized p-nitrophenol to a compound believed to be p-nitrophenyl glucoside-6-sulphate. None of the nine species of insect used was able to metabolize [14C]benzoic acid to a glucoside-phosphate or glucoside-sulphate conjugate.

Animals↗
PubMed1981

Inhibition of housefly oxidative detoxication by phthaleins, fluoresceins and related compounds.

1. Phenolphthalein, halogenated fluoresceins, and other triphenylmethane and diphenylmethane derivatives inhibited biphenyl hydroxylation, aldrin epoxidation and several O-dealkylations in insect abdomen homogenates. Phenolphthalein and eosin (50 muM) were 2-3 times more effective than SKF 525-A and piperonyl butoxide (50 muM) as inhibitors of biphenyl hydroxylation in vitro. 2. The phthaleins, Aurin and Aluminon, inhibited both epoxidation and hydroxylation to similar extents, but fluoresceins, Rhodamine B, Malachite Green, and basic diphenylmethane derivatives preferentially inhibited hydroxylation. 3. Tetrabromophenolphthalein ethyl ester and bis-(N-dimethyl-4-aminophenyl-methane inhibited biphenyl hydroxylation in vivo. Bis-(N-dimethyl-4-aminophenyl) methane synergized the toxic effects of 1-naphthyl N-methylcarbamate in live houseflies.

Abdomen↗
PubMed1976

Darwin's finches: population variation and natural selection.

Van Valen's model, which relates morphological variation to ecological variation in an adaptive scheme, was investigated with individually marked and measured Darwin's finches on two adjacent Galápagos islands, Santa Cruz and Daphne Major. Results show that environmental heterogeneity is correlated with large continuous, morphological variation: variation in bill dimensions of Geospiza fortis is greater on Santa Cruz than on Daphne, as is environmental heterogeneity. Within populations of this species, different phenotypes distribute themselves in different habitat patches, select foods of different sizes and hardness, and exploit them with efficiencies that are phenotype- (bill size) dependent. These data constitute indirect evidence that natural selection has a controlling influence over the level of phenotypic variation exhibited by a population. Further evidence is that phenotypes did not survive equally well during the study period; on Daphne island G. fortis was apparently subjected to directional selection on bill tip length and G. scandens to normalizing selection on body weight and bill depth. Other factors which may have contributed to the establishment of a difference in variation between Santa Cruz and Daphne populations are the founder effect, genetic drift, and assortative mating. Annual climatic unpredictability is considered a source of environmental heterogeneity which, through its effect upon food supply, favors large morphological variation. It is predicted that species of large individual size are more influenced by this than are small species, and consequently exhibit greater size-corrected variation. The prediction is tested with data from six Geospiza species, and found to be correct.

Adaptation, Biological↗
PubMed1974

Water-soluble metabolites of p-nitrophenol and 1-naphthyl N-methylcarbamate in flies and grass grubs. Formation of glucose phosphate and phosphate conjugates.

Metabolites isolated from houseflies dosed with 1-napththol or p-nitrophenol were identified as the phosphate and glucose phosphate conjugates of these phenols by titrations, hydrolysis, ionophoresis, i.r. spectra and mixed melting point. [(3)H]Carbaryl (1-naphthyl N-methylcarbamate) was metabolized by houseflies, blowflies and grass grubs to water-soluble metabolites which had chromatographic and ionophoretic behaviour similar to those of the conjugates of 1-naphthol with glucose, sulphate, phosphate and glucose 6-phosphate.

Animals↗
PubMed1973

Cross specificity in some vertebrate and insect glutathione-transferases with methyl parathion (dimethyl p-nitrophenyl phosphorothionate), 1-chloro-2,4-dinitro-benzene and s-crotonyl-N-acetylcysteamine as substrates.

1. Enzymes catalysing the reaction between GSH and methylparathion (dimethyl p-nitrophenyl phosphorothionate), 1-chloro-2,4-dinitrobenzene and S-crotonyl-N-acetylcysteamine were separated by (NH(4))(2)SO(4) precipitation from homogenates of sheep, rat and mouse livers and from homogenates of cockroaches, houseflies and grass grubs. 2. Electrofocusing of the preparations from each of these species separated a number of zones, each of which catalysed the reaction of GSH with all three substrates. 3. Ion-exchange chromatography on CM-cellulose also separated a number of fractions in which activity towards the three substrates coincided. 4. In both separation methods patterns of the activities were consistent with the presence in all species of several GSH transferases each having a degree of cross specificity towards the three substrates.

Animals↗