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Biomedical subjects

J C Turner

Publications and source records attributed to J C Turner.

At least 37 records · Page 2Linked to original sources
PubMed1989

High purity preparations of higher plant vacuolar H+-ATPase reveal additional subunits. Revised subunit composition.

A fast protein liquid chromatography procedure for purification of the V-type H+-ATPase from higher plant vacuolar membrane to yield near-homogeneous enzyme with a specific activity of 20-25 mumol/mg.min is described. When precautions are taken to ensure the quantitative recovery of protein before sodium dodecyl sulfate-polyacrylamide gel electrophoresis, the preparation is found to be constituted of seven major polypeptides of 100, 67, 55, 52, 44, 32, and 16 kDa, respectively, and two minor components of 42 and 29 kDa. The 52-, 44-, and 32-kDa polypeptides do not cross-react with antisera raised to the 67- and 55-kDa subunits of the enzyme, and two independent sample preparation procedures yield the same apparent subunit composition. The additional polypeptides are not breakdown products or aggregates of the previously identified subunits of the ATPase. The ATPase of tonoplast vesicles is subject to MgATP-dependent cold inactivation, and the conditions for inactivation are identical to those for the bovine chromaffin granule H+-ATPase (Moriyama, Y., and Nelson, N. (1989) J. Biol. Chem. 264, 3577-3582). Cold inactivation is accompanied by the detachment of five major polypeptides of 67, 55, 52, 44, and 32 kDa from the membrane, and all five components co-migrate with the corresponding polypeptides of the purified ATPase upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The 100- and 16-kDa polypeptides of the ATPase are not removed from the membrane during cold inactivation, but the latter can be purified to homogeneity by chloroform:methanol extraction of the fast protein liquid chromatography-purified enzyme. It is concluded that the tonoplast H+-ATPase is constituted of 6-7 major polypeptides organized into a peripheral sector comprising the 67-, 55-, 52-, 44-, and 32-kDa components and an integral sector consisting of the 100- and 16-kDa polypeptides. The V-type H+-ATPase from animal endomembranes and higher plant vacuolar membranes therefore have remarkably similar subunit compositions and gross topographies.

Chromatography, Gel↗
PubMed1987

Copper absorption in sheep.

Female sheep were used to determine the regions of the gastrointestinal tract able to absorb Cu. Copper was absorbed from the abomasum, small intestine and colon, but not from the rumen-reticulum or caecum. In vitro studies indicated that Cu uptake was linearly related to the Cu concentration. Copper complexed to histidine, lysine or glutamine was absorbed in a similar manner to ionic Cu and at a similar rate. In vitro Cu uptake was not affected by ouabain, rotenone, oligomycin, 2,4-dinitrophenol fluoride or zinc. The in vitro data show that lumen-to-mucosal cell Cu transfer has kinetics reflecting simple diffusion rather than a saturable, energy-dependent process.

Amino Acids↗
PubMed1987

Barley mutants lacking chloroplast glutamine synthetase-biochemical and genetic analysis.

Eight mutants of barley (Hordeum vulgare cv Maris Mink) lacking the chloroplast isozyme of glutamine synthetase (EC 6.3.1.2.) were isolated by their inability to grow under photorespiratory conditions. The cytoplasmic isozyme of glutamine synthetase was present in the leaves of all the mutants, with activities comparable to the wild-type (10-12 nanokatals per gram fresh weight). The mutant plants developed normally and were fully fertile under conditions that minimize photorespiration. In 1% O(2) the rate of CO(2) fixation in leaves of one of the mutants, RPr 83/32, was the same as the wild-type, but in air this rate declined to 60% of the wild-type after 30 minutes. During this time the ammonia concentration in leaves of the mutant rose from 1 to 50 micromoles per gram fresh weight. Such ammonia accumulation in air was found in all the mutant lines. In back-crosses with the parent line, F(1) plants were viable in air. In the F(2) generation, nonviability in air and the lack of chloroplast glutamine synthetase co-segregated, in both the lines tested. These two lines and four others proved to be allelic; we designate them gln 2a-f. The characteristics of these mutants conclusively demonstrate the major role of chloroplast glutamine synthetase in photorespiration and its associated nitrogen recycling.

Journal Article↗
PubMed1986

Effect of omega-trifluorination on the microsomal metabolism of ethyl and pent-1-yl p-nitrophenyl ether.

p-Nitrophenyl pent-1-yl ether was metabolized (65-70%) in the presence of liver microsomes from phenobarbital-treated rats to give the 4-(major), 3-(minor), and 2-hydroxypent-1-yl (minor) derivatives which were characterized by g.l.c.-mass spectrometry; O-dealkylation (reflecting 1-hydroxylation) and 5-hydroxylation did not occur to a significant extent. 5,5,5-Trifluorination of the pent-1-yl group markedly reduced the extent of metabolism (to approximately 10%). p-Nitrophenyl 2,2,2-trifluoroethyl ether was virtually completely resistant to microsomal metabolism under conditions where the ethyl analogue was extensively O-dealkylated.

Animals↗
PubMed1983

Effect of deuteration of imipramine on its pharmacokinetic properties in the rat.

Imipramine was specifically deuterated in either both aromatic rings or in the N-methyl group, or in both positions, and the pharmacokinetic properties of the products were determined in the rat and compared with those of the non-deuterated analogue. Deuteration of imipramine resulted in a small but significant isotope effect on N-demethylation while aromatic hydroxylation was unaffected. This isotope effect led to a slower rate of systemic clearance, a longer half-life and, when orally administered, enhanced bioavailability. Urinary excretion of didesmethylimipramine-d4, following oral administration of imipramine-d7, was significantly lower than the excretion of didesmethylimipramine following administration of unlabelled imipramine, indicating inhibited demethylation. Similarly, the urinary excretion of desmethylimipramine-d4, didesmethylimipramine-d4 and 2-hydroxydesmethylimipramine-d4 were lower than for the corresponding unlabelled or d7-analogues, indicating the stability of the N-CD3 group. Deuteration had no effect on the pharmacological properties of imipramine as determined in this study.

Animals↗
PubMed1982

An enzyme-linked immunoassay for pepsinogen in sheep plasma.

An enzyme-linked immunosorbent assay for pepsinogen in sheep plasma is described. The assay requires only 20 microliter of plasma. As little as 250 ng pepsinogen/ml plasma can be measured using antibody-coated polystyrene tubes and if "MicroElisa" plates are used 50 ng pepsinogen/ml plasma can be assayed. The method is more specific, more sensitive, uses less samples, has lower blank values than the present widely-used spectrophotometric method and could easily be automated.

Animals↗
PubMed1981

Bifluranol, a novel fluorinated bibenzyl anti-androgen, its chemistry and disposition in different animal species.

The synthesis of bifluranol, a new fluorinated bibenzyl anti-androgen, and of 3H-labelled bifluranol is described. The absorption, distribution and excretion of bifluranol has been studied in mouse, rat, ferret and dog; it is readily absorbed following oral administration, but blood concentrations of the drug are low due to hepatic uptake and biliary excretion. Enterohepatic re-circulation occurs, but the drug is excreted primarily in the faeces and only small amounts appear in urine. This pattern of disposition and excretion is similar to that reported elsewhere for the bibenzyl, hexoestrol, and for the stilbene, diethylstilboestrol.

Administration, Oral↗
PubMed1981

The metabolism of bifluranol by rat, dog and ferret.

The synthesis of monohydroxy- and dihydroxy-bifluranol, and of glucuronide and sulphate conjugates of bifluranol are described. Bifluranol administered orally to rats, ferrets and dogs at a dosage of 50 to 200 microgram kg-1 is mostly excreted in the faeces as unchanged bifluranol and bifluranol monosulphate, disulphate and monoglucuronide. The bifluranol is well absorbed and is mostly excreted in the bile, as six different conjugates, including a glucuronide sulphate found in all 3 species, and a glucuronide phosphate found only in ferret and dog bile. Hydroxylation of the aromatic rings occurs in the rat, to an extent of about 8% of the dose, but was not detected in ferret or dog.

Animals↗
PubMed1981

Interrelationships of glandular trichomes and cannabinoid content. II. Developing vegetative leaves of Cannabis sativa L. (Cannabaceae).

Gland number and cannabinoid content were quantified during ontogeny of vegetative leaves from three clones of Cannabis. Initiation of capitatesessile and bulbous glands was found to occur uniformly during leaf development. Cannabinoids were synthesized throughout leaf development as well, but at a decreasing rate. A positive correlation was found for total capitate-sessile glands per leaf as compared with total cannabinoid content of the leaf. The data also indicated that other leaf tissues in addition to the glands may contain cannabinoids.

Cannabinoids↗
PubMed1981

Interrelationships of glandular trichomes and cannabinoid content. I: Developing pistillate bracts of Cannabis sativa L. (Cannabaceae).

Gland number and cannabinoid content for three clones of Cannabis were compared. Cannabinoid levels and mature glands were quantified throughout progressive stages of pistillate bract development in order to define possible interrelationships between glands and cannabinoids. Similar trends occurred among the clones for each gland type while individual cannabinoids displayed a different pattern in each clone. Gland initiation and development as well as cannabinoid synthesis were found to occur during bract ontogeny for all three clones. A positive correlation existed for the total number of capitate glands per bract compared to the total cannabinoid content of the bract. The study also suggested that the glands may contain the majority of the cannabinoids present in the bract.

Cannabinoids↗