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Biomedical subjects

A Taylor

Publications and source records attributed to A Taylor.

At least 613 records · Page 34Linked to original sources
PubMed1987

High level expression of proinsulin in the yeast, Saccharomyces cerevisiae.

Human proinsulin (PI) has been expressed to a high level (100 mg/liter) as a human superoxide dismutase-PI fusion protein in the yeast, Saccharomyces cerevisiae. At the junction of the two proteins is a methionine residue, allowing PI to be released from the fusion by reaction with cyanogen bromide. The fusion is expressed using a regulated, hybrid promoter containing the regulatory region of the alcohol dehydrogenase II promoter and the 3' end of a glyceraldehyde-3-phosphate dehydrogenase promoter, allowing the recombinant yeast cells to be stably maintained. Production of the fusion protein is induced by growth in medium lacking a fermentable carbon source. The heterologous fusion protein is probably insoluble within the cell, since electron microscopy reveals the presence of 'inclusion bodies'. In a cell-free extract the fusion protein is also insoluble, but can be solubilized with sodium dodecyl sulfate, and cleaved with cyanogen bromide. The PI that is produced contains incorrect disulfide bonds. After sulfitolysis, the product can be easily purified, renatured, and processed to yield insulin.

Chromosome Mapping↗
PubMed1987

Protein oxidation and loss of protease activity may lead to cataract formation in the aged lens.

Over 95% of the dry mass of the eye lens consists of specialized proteins called crystallins. Aged lenses are subject to cataract formation, in which damage, cross-linking, and precipitation of crystallins contribute to a loss of lens clarity. Cataract is one of the major causes of blindness, and it is estimated that over 50,000,000 people suffer from this disability. Damage to lens crystallins appears to be largely attributable to the effects of UV radiation and/or various active oxygen species (oxygen radicals, 1O2, H2O2, etc.). Photooxidative damage to lens crystallins is normally retarded by a series of antioxidant enzymes and compounds. Crystallins which experience mild oxidative damage are rapidly degraded by a system of lenticular proteases. However, extensive oxidation and cross-linking severely decrease proteolytic susceptibility of lens crystallins. Thus, in the young lens the combination of antioxidants and proteases serves to prevent crystallin damage and precipitation in cataract formation. The aged lens, however, exhibits diminished antioxidant capacity and decreased proteolytic capabilities. The loss of proteolytic activity may actually be partially attributable to oxidative damage which proteases (like any other protein) can sustain. We propose that the rate of crystallin damage increases as antioxidant capacity declines with age. The lower protease activity of aged lens cells may be insufficient to cope with such rates of crystallin damage, and denatured crystallins may begin to accumulate. As the concentration of oxidatively denatured crystallins rises, cross-linking reactions may produce insoluble aggregates which are refractive to protease digestion. Such a scheme could explain many events which are known to contribute to cataract formation, as well as several which have appeared to be unrelated.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1987

Effect of thyroxine replacement therapy on plasma insulin-like growth factor 1 levels and growth hormone responses to growth hormone releasing factor in hypothyroid patients.

The aim of this study was to evaluate the effect of T4 replacement therapy on plasma insulin-like growth factor 1 (IGF-1) levels in patients with primary hypothyroidism to see whether recovery of pituitary GH responsiveness to GRF was associated with increased plasma IGF-1 levels. IGF-1 levels and GH responses to GRF (1 microgram/kg) were measured in 21 patients with primary hypothyroidism before and after T4 replacement therapy. T4 increased plasma IGF-1 levels (57.2 +/- 4.4 vs 75.9 +/- 8.8 ng/ml, mean +/- SEM, P less than 0.05) and GH responses to GRF as assessed both by peak GH levels (9 +/- 1.5 ng/ml before treatment vs 16.7 +/- 3 ng/ml after treatment, mean +/- SEM, P less than 0.05) and area under curve (496 +/- 92 before treatment vs 896 +/- 161 after treatment, mean- +/- SEM, P less than 0.05). Linear regression analysis showed a positive correlation between free T3 and IGF-1 levels after treatment (r = 0.37, P less than 0.05) and a negative relationship between plasma IGF-1 levels before treatment and delta IGF following T4 replacement therapy (r = 0.45, P less than 0.025). However, no correlation was found between plasma IGF-1 levels and GH responses to GRF, suggesting that GH responses to GRF are of no predictive value in relation to the recovery of plasma IGF-1 levels following T4 replacement therapy in hypothyroid patients.

Adult↗
PubMed1987

The antibacterial activity of alamethicins and zervamicins.

Consistent results were obtained in biological assays of alamethicins on agar gels only when the antibiotics were allowed to diffuse under strictly defined conditions of temperature and time before inoculation. In liquid culture obligatory anaerobic rumen bacteria were sensitive to these antibiotics and in certain cases their ability to produce volatile fatty acids was reduced. Among the bacteria examined there was a 1000-fold difference in their sensitivity. Modifications of the structure of the peptaibol, e.g. substitution of an alanine residue for a 2-methylalanine residue resulted in ca two-fold changes in activity.

Alamethicin↗
PubMed1987

New developments with the heavy metal vapor lasers for the dermatologist.

In controlled studies the heavy metal vapor lasers are important for dermatologic surgery, for vascular lesions, and for skin malignancies, especially those malignancies which cannot be treated by conventional means. The flexibility of the fiberoptic system for transmitting the lasers lends itself to laser vascular surgery, cancers of the skin, and mucous membranes. The heavy metal vapor laser is one of the few laser systems for clinical practice which include two different systems, thereby increasing applications.

Copper↗
PubMed1987

Membranous nephropathy caused by mercury-containing skin lightening cream.

A 46 year old woman developed membranous nephropathy following the use of a mercury-containing skin lightening cream. This association has not been reported in the literature for over a decade and apparently never from this country. It is important that clinicians are aware of this usually eminently treatable cause of the nephrotic syndrome as it is likely to be missed unless specifically enquired for.

Basement Membrane↗
PubMed1987

The production of alamethicins by Trichoderma spp.

The production of polypeptides containing a high percentage of 2-methylalanine residues by a number of isolates of Trichoderma spp. has been examined. It has been shown that good yields (0.5-1.0 g L-1) can be achieved on synthetic media provided an insoluble carbohydrate is included and provided single-spore isolates that have this production ability are selected from time to time. Such yields could not be obtained on any single nitrogen source investigated, but a mixture of potassium nitrate, glutamine, and 2-methylalanine was effective. It was shown that at least eight polypeptides were produced in shake-flask or tank fermentation and that the proportions of these metabolites depended on the fermentation temperature, its pH, age, and aeration. Fermentation conditions for enhancing the production (independently) of two of the metabolites at the expense of the others are given. These two metabolites have been obtained in crystalline form and details of some of their physical and chemical properties are given.

Alamethicin↗
PubMed1987

Evaluation of Tc-99m mercaptoacetyltriglycine in patients with impaired renal function.

Technetium-99m mercaptoacetyltriglycine (MAG3), a new radiopharmaceutical shown to have biological properties similar to iodine-131 o-iodohippurate (OIH) in animals and healthy volunteers, was compared with OIH in 15 patients with varying degrees of renal impairment. The Tc-99m MAG3 images were uniformly superior, regardless of the serum creatinine level. There was no significant difference in the 30-minute blood clearance of OIH and MAG3. MAG3 protein binding (78.6%) was greater than that of OIH (53.1%) (P less than or equal to .01), and the volume of distribution of MAG3 (7.06 liters) was less than that of OIH (10.78 liters) (P less than or equal to .01). In six patients the 30-minute urinary excretion of the two agents was essentially identical. The time to the peak height of the renogram curves was more rapid for MAG3 than for OIH using both cortical and whole-kidney regions of interest (P less than or equal to .02). In summary, preliminary results suggest that Tc-99m MAG3 performs well in patients with impaired renal function and may well be an acceptable replacement for OIH. A kit formulation is currently undergoing clinical evaluation.

Blood Proteins↗
PubMed1987

Cytosolic calcium and the action of vasopressin in toad urinary bladder.

The effects of experimental procedures believed to increase cytosolic calcium on basal and vasopressin-stimulated osmotic water flow and transepithelial sodium transport were examined in the toad urinary bladder. Exposure of isolated toad bladders to quinidine, calcium ionophores (A23187, X537A), or low-sodium or potassium-free serosal solutions resulted in a dose-dependent decrease in the hydrosmotic response to vasopressin or exogenous adenosine 3',5'-cyclic monophosphate (cAMP). The degree of inhibition of cAMP-induced water flow induced by low-sodium or potassium-free serosal bathing media varied, and in a similar manner, with the serosal calcium concentration. The effects of quinidine sulfate (2 X 10-4 M), X537A (2 X 10(-5) M), and low serosal sodium (20 mM), but not that of A23187 (10(-5) M), were readily reversible. Exposure to quinidine (4 X 10(-4) M), A23187 (10(-5) M), X537A (5 X 10(-6) M), or low serosal sodium (2 mM) also inhibited the basal short-circuit current (SCC). Vasopressin, 4-20 mU/ml, completely overcame the inhibition of the SCC induced by quinidine, A23187, or low serosal sodium, but a submaximal dose of hormone (4 mU/ml) failed to fully reverse the inhibitory effect of X537A, 5 X 10(-6) M. These results are consistent with the view that 1) a Na-Ca exchange process operates across the basolateral surface of the granular epithelial cells of the toad urinary bladder in vivo, and 2) the level of free calcium in the granular cell cytosol plays a modulatory role in the control of apical membrane water and sodium permeability by vasopressin, and in the regulation of the basal rate of transepithelial sodium transport.

Animals↗
PubMed1987

Quinidine effect on hydrosmotic response of collecting tubules to vasopressin and cAMP.

Quinidine, a compound thought to increase cytosolic calcium ion activity, has been found to inhibit the hydrosmotic response to vasopressin (VP) and adenosine 3',5'-cyclic monophosphate (cAMP) in the toad urinary bladder. To test whether this drug has a similar action in the mammalian nephron, the effect of quinidine on the hydraulic conductivity of the isolated perfused rabbit cortical collecting tubule (CCT) exposed to either 20 microU/ml VP or 10(-4) M 8-(p-chlorophenylthio) - adenosine 3',5' - cyclic monophosphate (8-CPT-cAMP) was studied. Quinidine had no effect on the basal water permeability of the CCT. Quinidine sulfate (10(-4) M) reduced the VP-stimulated water permeability from 280 +/- 50 X 10(-7) to 115 +/- 41 X 10(-7) cm X s-1 X atm-1 (P less than 0.05). The hydrosmotic response to 8-CPTcAMP was likewise reduced following exposure to quinidine. This effect was shown to be dose dependent. In paired experiments, inhibition of the response to 10(-4) M 8-CPTcAMP averaged 11% at 10(-6) M, 27% at 5 X 10(-6) M, 53% at 5 X 10(-5) M, and 50% at 10(-4) M quinidine. Inhibition of the response to 8-CPTcAMP was estimated to be half maximal at approximately 5 X 10(-6) M quinidine. Tubules were protected against the quinidine-induced inhibition by the addition of 6.5 X 10(-5) M quin 2-acetoxymethylester in the presence of low peritubular Ca concentration. These results are consistent with the view that elevated cytosolic Ca ion levels inhibit the increase in water permeability elicited by VP or exogenous cAMP in the mammalian CCT.

Animals↗
PubMed1987

Erythrocyte fatty acid profiles in patients with bronchogenic carcinoma.

The use of the erythrocyte stearic:oleic acid ratio in the diagnosis and prognosis of bronchogenic carcinoma has been assessed. Although there was a significant difference (P less than 0.02) in the erythrocyte stearic:oleic acid ratio between bronchogenic carcinoma patients and healthy adults, the large overlap observed in the two groups rendered the test unsuitable for the diagnosis of malignancy. Furthermore, there was no consistent rise in this ratio after surgical resection, indicating the test to be of little prognostic use. A new explanation for the lower stearic:oleic acid ratios in certain patients has been postulated.

Adult↗
PubMed1987

Arginine vasopressin and oxytocin in the bovine adrenal gland.

The concentrations of immunoreactive oxytocin and arginine vasopressin (AVP) and their respective neurophysins (NpI and NpII) were compared in bovine adrenal cortex and medulla. While the concentration of AVP was similar in both tissues there was more NpII in the medulla. The medulla also contained much more oxytocin and NpI than the cortex. The extracted AVP and oxytocin had identical retention times to those of the synthetic peptides on high-performance liquid chromatography (HPLC) and were biologically active in assays for antidiuretic and milk-ejection activity (with potencies of 310 units/mg and 340 units/mg respectively). Adrenal NpI and NpII behaved identically to commercially available neurohypophysial proteins on HPLC. Oxytocin, NpI and AVP were assayed in five subcellular fractions of bovine adrenal medulla prepared on discontinuous sucrose gradients. A high proportion of each co-localized with noradrenaline and adrenaline in the chromaffin granule fraction. Binding of [3H]AVP and [3H]oxytocin to crude bovine adrenal medulla membranes was dependent upon both time and temperature. The binding sites were specific and saturable: studies with the V1 AVP antagonist d(CH2)5Tyr(Me)AVP and the V2 agonist 1-deamino-8-D-AVP indicated that the AVP receptor was V1 in specificity. Scatchard plots showed that each ligand interacted with a single high-affinity, low-capacity binding site: oxytocin dissociation constant (Kd) 3.1 +/- 0.29 nmol/l, maximum binding capacity (Bmax) 89.6 +/- 18.4 fmol/mg protein (n = 3); AVP Kd 0.73 +/- 0.02 nmol/l, Bmax 26.5 +/- 8.3 fmol/mg protein (n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗
PubMed1987

The in vitro replicative potential and cellular morphology of human lens epithelial cells derived from different aged donors.

Cultures of human lens epithelial cells have been established using explants of the lens capsule from different aged donors. Outgrowth from the explants occurs more quickly using material from younger as opposed to older donors. The total number of cells as well as the cumulative surface area covered by cell growth is more extensive with the explants from the lens capsules of younger donors as compared with the amount of cell growth from older donor lens capsules. Thus, there is an inverse correlation between donor age and the replicative capacity of human lens epithelial cells in vitro. The lens epithelial cell cultures from human donors of all ages have a finite replicative potential.

Adolescent↗
PubMed1987

Animal evaluation of technetium-99m triamide mercaptide complexes as potential renal imaging agents.

Technetium-99m mercaptoacetylglycylglycylglycine (MAG3), a [99mTc]triamide mercaptide (N3S) compound has been synthesized in an attempt to obviate the stereochemistry problems associated with the diamide dimercaptide (N2S2) ligands. Because initial studies have been promising, the terminal glycine on the MAG3 compound has been varied to create a new series of N3S compounds. Twelve new N3S complexes were initially screened in mice and the more promising complexes, 99mTc mercaptoacetylgylcylglycyl-glycine [( 99mTc]MAG3), 99mTc mercaptoacetylgylcylglycyl-L-alanine [( 99mTc]MAG2-Ala), and both complexes of 99mTc mercaptoeacetylglycylglycyl-L-asparagine [( 99mTc]MAG2-Asn) and 99mTc mercaptoacetylglycylglycyl-L-glutamine [( 99mTc]MAG2-Gln), were further evaluated in rats utilizing constant infusion blood clearances, extraction efficiencies and protein binding assays. The renal excretion of all these complexes compared favorably with simultaneously administered [131I]OIH and [125I]iothalamate. The triamide mercaptide complexes represent a new ligand class for 99mTc, which may provide a variety of complexes for the evaluation of renal tubular function.

Animals↗