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S Webber

Publications and source records attributed to S Webber.

71 records · Page 4Linked to original sources
PubMed1986

Preliminary x-ray diffraction characterization of crystalline rat liver dihydropteridine reductase.

The pyridine dinucleotide-dependent dihydropteridine reductase from rat liver has been crystallized from various inorganic salts and from polyethylene glycol/ethanol mixtures using a vapor diffusion method. The crystal form most amenable to x-ray diffraction studies is monoclinic, space group C2, a = 224.3 A, b = 46.5 A, c = 94.9 A, beta = 99.0 degrees with two molecules in the crystallographic asymmetric unit. These crystals grow to over 1 mm in length, diffract to at least 2.3 A resolution, and are relatively stable to irradiation with x-rays.

Animals↗
PubMed1986

Multiple forms of rat-liver dihydropteridine reductase identified by their differing isoelectric points.

Purified rat-liver dihydropteridine reductase is homogeneous by gel filtration (Mr approximately 51,000), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Mr approximately 25,500), and native polyacrylamide gel electrophoresis, suggesting that the enzyme is composed of two identical subunits. However, analysis by isoelectric focusing has revealed three enzyme forms with approximate isoelectric points of 6.5, 5.9, and 5.7 (designated forms, I, II, and III, respectively). The three forms, isolated in 65% yield by preparative chromatofocusing, are stable in 0.05 M phosphate buffer, pH 6.8, containing 1 mM beta-mercaptoethanol and exhibit similar kinetic constants when the catalytic activities of the isolated forms are compared with quinonoid dihydrobiopterin as substrate. All forms generate complexes with the enzymatic cofactor NADH which are also detectable by IEF. When examined further by IEF under denaturing conditions in 6 M urea the enzyme demonstrates a differing subunit composition for its three forms. Two distinct subunits, designated alpha and beta, can be identified, and additional evidence suggests that the native enzyme forms I, II, and III represent the three differing dimeric combinations alpha alpha (form I), alpha beta (form II), and beta beta (form III).

Animals↗
PubMed1986

Synthesis and efficient isolation procedure for gamma-linked fluorescein methotrexate.

Fluorescein isothiocyanate was reacted in dimethyl sulfoxide with a ten-fold excess of diaminopentane, and the mono-substituted thiourea product was isolated by DEAE-cellulose chromatography, lyophilization and acid precipitation from aqueous base. The dried product was then condensed in dry dimethyl sulfoxide with Methotrexate (MTX) activated by prior incubation (30 min) with 1-ethyl-3-(3'-dimethylaminopropyl) carbodiimide hydrochloride, and the reaction products were purified by column chromatography on DEAE-cellulose. Exhaustive elution with 1 M ammonium bicarbonate removed several by-products then finally afforded the exclusively gamma-linked fluorescein--MTX derivative. After lyophilization and acid-base precipitation the compound was obtained in good yield (greater than 40%), was homogeneous by reverse-phase HPLC epsilon 493 (0.1 N NaOH) = 66,000 and was a comparable inhibitor to MTX for rat-liver dihydrofolate reductase.

Animals↗
PubMed1985

Comparative activity of rat liver dihydrofolate reductase with 7,8-dihydrofolate and other 7,8-dihydropteridines.

The various interactions of rat liver dihydrofolate reductase with two unconjugated 7,8-dihydropteridines, 7,8-dihydrobiopterin and 6-methyl-7,8-dihydropteridine, have been compared with those of 7,8-dihydrofolate and folate. Of particular interest was the reactivity demonstrated by 7,8-dihydrobiopterin because of the potential physiological significance of this reaction both in the regeneration of tetrahydrobiopterin, a cofactor for various biological hydroxylations, and as a step in the biosynthesis of this compound from GTP. Kinetic experiments gave Km values of 0.17, 6.42, and 10.2 microM for 7,8-dihydrofolate, 7,8-dihydrobiopterin, and 6-methyl-7,8-dihydropteridine, respectively, with Vmax = 6.22, 2.39, and 1.54 mumol min-1 mg-1. With folate the enzyme showed high affinity (Km = 0.88 microM) but low Vmax (0.20 mumol min-1 mg-1). The natural cofactor was NADPH and a Km of approximately 0.7 microM was measured with each substrate. The enzyme was activated by both p-hydroxymercuribenzoate and urea when assayed with 7,8-dihydrofolate but was inhibited when 7,8-dihydrobiopterin was the substrate. The pH optimum for dihydrofolate reduction was 4 with enhancement at pH greater than or equal to 5.5 in the presence of 1 M NaCl. Peak activity with 7,8-dihydrobiopterin occurred at pH 4.8; this was shifted to pH 5.3 but was not enhanced by 1 M NaCl. Inhibition with methotrexate was similar whether the enzyme was assayed with either the conjugated or unconjugated 7,8-dihydro derivatives. The rat liver enzyme, highly unstable after purification, was stabilized in the presence of the nonionic detergent, Tween-20 (0.1%); however, the comparative properties toward the conjugated and unconjugated substrates were not altered by this treatment.

Animals↗
PubMed1985

Student health during overseas electives.

Ill health is often encountered by travellers. As medical students are encouraged to spend their electives overseas, it was considered worthwhile to study the morbidity experience of University of Bristol medical students and to see whether any additional preventive measures could be identified for them. The findings suggest that the quality of advice could be further improved for medical students undertaking their electives abroad. Additional preventive measures were suggested by the students themselves. The suggestions may also be useful for other groups of travellers.

Health Status↗
PubMed1984

An abbreviated synthesis of tetrahydropteridines.

5,6,7,8-Tetrahydrobiopterin, the naturally occurring essential cofactor for the enzymatic hydroxylations of phenylalanine, tyrosine and tryptophan, and its synthetic analog 2-amino-6-methyl-5,6,7,8-tetrahydro-4(3H)-pteridinone, have been synthesized in good yield by the direct hydrogenation of 1-(2-amino-1,6-dihydro-5-nitro-6-oxopyrimidin-4-yl-amino)-1,5-dide oxy-L- erythro-pentulose and 2-amino-6-hydroxy-5-phenylazo-4-pyrimidylamino-acetone, respectively. The reactions were carried out at room temperature in trifluoroacetic acid over a platinum catalyst at 2 atm and the products, each containing a mixture of the two possible C-6 isomers, were isolated by precipitation. The simplicity of the preparative method suggests the procedure may be applied generally to the synthesis of all tetrahydropteridines derived from similar pyrimidine precursors.

Biopterins↗
PubMed1978

Pyridine nucleotide interaction with rat liver dihydropteridine reductase.

The interactions of a homogeneous preparation of rat liver dihydropteridine reductase with NADH, NADPH, NAD+, NADP+, and the 1-N6-ethenoadenine derivative of NAD+ have been investigated by fluorescence titration, circular dichroism, equilibrium dialysis, Sephadex G-25 chromatography, and polyacrylamide gel electrophoresis. The procedures indicate that the dimeric enzyme has a definite preference for NADH, but binds only 1 mol of this nucleotide per mol of enzyme. The binary complex of enzyme with NADH is only partially stable to exhaustive dialysis and gel electrophoresis, where it shows greater mobility (0.26) than the free enzyme (0.21); however, the complex can be isolated by Sephadex G-25 chromatography, and characterized with respect to its absorbance spectrum. No ternary complexes are observed when samples of reductase, preincubated with excess NADH, and either the reaction product, 2-amino-4-hydroxy-6,7-dimethyl-5,6,7,8-tetrahydropteridine, or the inhibitor, methotrexate, are subjected to polyacrylamide gel electrophoresis.

Animals↗
PubMedDate not supplied

Descending aortic blood flow velocity as a noninvasive measure of cardiac output in children.

In previous work, we postulated that mean aortic flow velocity (MAFV) might be a direct measure of cardiac index. To investigate the assumptions inherent in this relation, we measured body surface area, aortic cross-sectional area (two-dimensional ultrasonography) and MAFV (Doppler ultrasonography) in 70 normal children. For a direct check of the relation, we simultaneously measured cardiac index (Fick technique) and MAFV (Doppler ultrasonography) in 25 children after cardiac surgery. In the normal group, we found that body surface area was directly proportional to aortic cross-sectional area (R 0.94), and MAFV at rest was the same in the ascending and descending aorta (t test, p < 0.05). In the intensive care patients, MAFV in the descending aorta was directly proportional to cardiac index over a wide clinical range [MAFV (cm/s) = CI (L/min/m2).7.7-1.2]. The assumptions made when deriving the relation between MAFV and cardiac index appear to be valid whether measured in the ascending or descending aorta. However, the scatter of results limits its clinical value. Mean aortic flow velocity is probably of greater use as a trend indicator and has the potential for continuous display using an esophageal Doppler probe when measured in the descending aorta.

Adolescent↗
PubMedDate not supplied

Antitumor efficacy of AG3340 associated with maintenance of minimum effective plasma concentrations and not total daily dose, exposure or peak plasma concentrations.

Oral administration of AG3340, a novel metalloprotease (MMP) inhibitor, suppresses the growth of human colon adenocarcinoma (COLO-320DM) tumors in vivo (Proc Am Assoc Cancer Res 39: 2059, 1998). In this report, we tested the hypothesis that the growth inhibition of these tumors is associated with maintaining minimum effective plasma concentrations of AG3340. Nude mice were given a total oral daily dose of 25 or 200 mg/kg; 6.25 mg/kg was given four times per day (QID) (25 mg/kg/day), and 100 mg/kg was given in two daily doses (BID) (200 mg/kg/day). Peak plasma concentrations (Cmax) of 83 +/- 43 (mean +/- SD) and 1998 +/- 642 ng/ml were detected 30 min after a single dose with 6.25 mg/kg and 100 mg/kg AG3340, respectively. AUC(0-24 h) values estimated from dosing with 25 and 200 mg/kg/day AG3340 were 672 and 10882 ng*h/ml, respectively. Importantly, both regimen inhibited tumor growth equivalently (74 to 82%). Efficacy was also compared at a total daily dose of 25 mg/kg by giving AG3340: QID (6.25 mg/kg per dose), BID (12.5 mg/kg per dose), and once daily (25 mg/kg per dose). The Cmax of these regimens was 83 +/- 43, 287 +/- 175 and 462 +/- 495 ng/ml, respectively. AG3340 did not inhibit tumor growth with the latter two regimens. The efficacy of 6.25 mg/kg QID (25 mg/kg/day) was superior to the efficacy of 25 mg/kg BID (50 mg/kg/day), substantiating the independence of efficacy from the total daily dose and Cmax. Expectedly, peak to trough fluctuations were significantly smaller with the QID regimen than with BID and QD dosing. After 24 h, the trough was greater than 1 ng/ml with QID dosing but was less than 1 ng/ml after QD and BID dosing. These results suggest that the antitumor efficacy of AG3340 was associated with maintaining minimum effective plasma concentrations of AG3340 and demonstrate that the antitumor efficacy of AG3340 was independent of the total daily dose, peak plasma concentration, and drug exposure in this tumor model.

Animals↗
PubMedDate not supplied

IFN-gamma production from human Th1 cells is controlled by Raf kinase.

Raf kinase is an important intracellular mediator in T cell signalling and may be crucial for the proliferation of this inflammatory cell. In order to elucidate its effect on cytokine production by human T cells in response to T cell receptor activation, experiments were carried out on human T cell clones using antisense (AS) oligodeoxynucleotides (ODN) to inhibit the expression of Raf kinase. AS ODN to Raf were shown to have a significant effect on a human Th1-like T cell clone, inhibiting antiCD3-induced IFN-gamma secretion by 76%, whereas no inhibitory effect was observed on IL-5 or IL-4 production by a Th2-like clone. IL-2 secretion from both clones was also not affected by the Raf AS ODN. In all cases, a reduction in Raf kinase within the cell was demonstrated by Western blot. Our results clearly demonstrate the importance of Raf kinase in the production of IFN-gamma from Th1 cells, but also show the lack of effect of this intracellular mediator on cytokine (IL-5, IL-4) release from Th2 cells.

Humans↗
PubMedDate not supplied

Cluster staffing: cooperation, competence, and caring.

1. A very large OR staff that deals with a multitude of specialty areas may find it difficult to keep up skill and knowledge levels in all areas. This may lead to staff dissatisfaction and a high turnover rate. 2. Partially by allowing staff to chose their own clusters, cluster staffing works to increase staff satisfaction, to increase the clinical knowledge "comfort zone," to improve efficiency, and to reduce the turnover rate. 3. The results of cluster staffing at the University of Massachusetts Medical Center indicate that staff are happier, are more relaxed, focus more on patient care, and work together more efficiently.

Humans↗