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A D Robertson

Publications and source records attributed to A D Robertson.

At least 55 records · Page 3Linked to original sources
PubMed1996

Temperature and pH dependences of hydrogen exchange and global stability for ovomucoid third domain.

Two-dimensional nuclear magnetic resonance spectroscopy has been used to monitor proton-deuterium exchange rates (kobs) for more than 30 residues in turkey ovomucoid third domain. To test whether exchange is governed by global unfolding, rates were measured over a wide range of pH and temperatures where the change in the free energy of unfolding (delta Gzerou) is known [Swint, L., & Robertson, A. D. (1993) Protein Sci. 2, 2037-2049; Swint-Kruse, L., & Robertson, A. D. (1995) Biochemistry 34, 4724-4732]. Under conditions where EX2 kinetics are observed, a subset of 6-11 residues exhibits a one-to-one correlation with global stability. These residues are all located in central regions of secondary structures. Many other sites show varied degrees of correlation with delta Gzerou, while some are slower than expected on the basis of delta Gzerou alone. Preliminary evidence suggests that the latter is due to deviation from EX2 kinetics, even though experimental conditions are relatively mild (pH* 3 and 40 degrees C) compared to those in which deviations were observed for bovine pancreatic trypsin inhibitor. These results, together with similar observations for hen egg white lysozyme and barnase, suggest that EX2 kinetics should not be assumed when interpreting exchange studies.

Amino Acid Sequence↗
PubMed1996

Synthesis of Hexahydrocyclopentimidazol-2-(1H)-one derivatives displaying selective DP-receptor agonist properties.

The rationale for investigating conformationally restricted analogues of BW245C as DP-receptor ligands and the syntheses of three such racemic bicyclic imidazolidinone analogues are described. Compounds 7 (BW587C), 8 (BW480C85), and 9 (BW572C85) were found to be potent inhibitors of human platelet aggregation and selective DP-receptor agonists in washed platelet and jugular vein isolated tissue assays.

Animals↗
PubMed1996

Serum and urinary interleukin-6 in systemic lupus erythematosus.

Dysregulation of IL-6 production has been proposed as a pathogenic mechanism in SLE. We asked if serum or urine IL-6 levels could serve as indicators of systemic lupus erythematosus (SLE) disease activity. Using a sensitive enzyme-linked immunosorbent assay (ELISA), we measured serum and urine IL-6 in 56 SLE patients. Disease activity was assessed using a standard clinical index, the Systemic Lupus Activity Measure (SLAM). Only seven of 56 SLE patients had elevated serum IL-6 levels, compared with 1 of 32 controls (NS). SLE disease activity did not correlate with serum IL-6 levels. Sixteen of 50 SLE patients in whom urine IL-6 was measured exhibited elevated urine IL-6 levels, compared with 1 of 17 controls (p = < 0.05). Urine IL-6 levels correlated with overall disease activity and with the presence of active urinary sediment. Our results indicate that serum IL-6 is not a predictor of disease activity in SLE, but that urine IL-6 may be a marker of active nephritis.

Adult↗
PubMed1995

Effects of a naturally occurring compatible osmolyte on the internal dynamics of ribonuclease A.

Osmolytes are small organic solutes accumulated intracellularly by many organisms as they adapt to environmental stresses. Compatible osmolytes, a functional class of osmolytes, increase protein stability while having little or no effect on protein function. To investigate the interrelationships between protein stability, function, and internal dynamics, a hydrogen exchange (HX) quench method was established and used to study the effects of sucrose (a typical compatible osmolyte) on the structural fluctuations of ribonuclease A. It was found that the HX rates of the amide protons with intermediate rates are not affected by 1 M sucrose, but the slow-exchanging amide protons exchange even slower in 1 M sucrose. The protection factors of the slow-exchanging protons fall into a comparatively narrow range while those of the intermediate-exchanging protons vary widely. In agreement with the two-process model [Woodward, C.K., & Hilton, B. D. (1980) Biophys. J. 32, 561-575], we conclude that for those slow-exchanging amide protons, the exchange occurs mainly from the compact unfolded state ensemble of the protein. The internal dynamics leading to slow exchange involve exposure of large protein surface areas, similar to that which occurs upon the unfolding of protein. Because sucrose opposes such an increase in protein surface area exposure, both the slow HX rates and the protein stability are affected by sucrose. For those amide protons with fast and intermediate HX rates, the exchange occurs mainly from the native state ensemble of the protein. The internal dynamics involved in the exchange are localized without much surface area change, and functionally important structural fluctuations are likely to occur within this dynamic range.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Computer-aided design and synthesis of 5-substituted tryptamines and their pharmacology at the 5-HT1D receptor: discovery of compounds with potential anti-migraine properties.

The design and synthesis of a series of novel 5-substituted tryptamines with pharmacological activity at 5-HT1D and other monoamine receptors is described. Structural modifications of N- and C-linked (principally hydantoin) analogues at the 5-position were synthesized and their pharmacological activities were utilized to deduce significant steric and electrostatic requirements of the 5-HT1D and 5-HT2A receptor subtypes. Conformations of the active molecules were computed which, when overlaid, suggested a pharmacophore hypothesis which was consistent with the affinity and selectivity measured at 5-HT1D and 5-HT2A receptors. This pharmacophore is composed of a protonated amine site, an aromatic site, a hydrophobic pocket, and two hydrogen-bonding sites. A "selectivity site" was also identified which, if occupied, induced sensitivity for 5-HT1D over 5-HT2A in this series of molecules. The development and use of the pharmacophore models in compound design is described. In addition, the physicochemical constraints of molecular size and hydrophobicity required for efficient oral absorption are discussed. Utilizing the pharmacophore model in conjunction with the physicochemical constraints of molecular size and log DpH7.4 led to the discovery of 311C90 (6), a new selective 5-HT1D agonist with good oral absorption and potential use in the treatment of migraine.

Animals↗
PubMed1995

Cold denaturation of CheY.

The thermal stability of the bacterial chemotaxis protein CheY from Salmonella typhimurium has been examined by thermal denaturation at pH 7.0 in the presence of guanidine-HCl and urea. For both denaturants, thermal denaturation monitored by circular dichroism spectropolarimetry consists of transitions both above and below 25 degrees C, which is strong evidence for a heat capacity change that is > or = 1500 cal/(mol K) upon unfolding. While many data for chemical and thermal denaturation are consistent with data for CheY from Escherichia coli, the observation of cold denaturation for S. typhimurium CheY is inconsistent with the small heat capacity change, 600 to 850 cal/(mol K), reported for denaturation of the E. coli protein.

Bacterial Proteins↗
PubMed1995

pH, ionic strength, and temperature dependences of ionization equilibria for the carboxyl groups in turkey ovomucoid third domain.

Two-dimensional NMR spectroscopy has been used to monitor the pH dependences of proton chemical shifts for turkey ovomucoid third domain (OMTKY3). Sample pH was varied from 7.0 to 1.4 in order to determine the apparent pKa values of all six carboxyl groups in OMTKY3. At 35 degrees C and in the presence of 10 mM KCl, the pKa values for Asp 7, Glu 19, and Asp 27 (< 2.6, 3.2, and < 2.3, respectively) are more than 1 pH unit below those for model compounds. The pKa values for Glu 10 (4.1) and Glu 43 (4.7) show more modest deviations from model compound data. The low pKa for the alpha-carboxyl group of Cys 56 (< 2.5) is attributable, at least in part, to acidification by the disulfide group. Fitting the data to a modified Hill equation [Markley, J. L. (1975) Acc. Chem. Res. 8, 70-80] reveals little evidence for interactions between the acidic groups; most Hill coefficients fall between 0.8 and 1.2, with outlying values usually obtained with data that describe incomplete transitions. Most of the very low pKa values show increases in the presence of 1.0 M KCl but, with the exception of that for glutamate 19, remain well below model compound values. pH-dependent changes in amide proton chemical shifts permitted identification of hydrogen bonds involving the side chains of Asp 7, Glu 19, and Asp 27, which may partially explain the low pKa values for these groups. These hydrogen bonds, two of which involve side chains that are well exposed to solvent, were previously identified in high-resolution X-ray studies of turkey ovomucoid third domain [Fujinaga, M., Sielecki, A. R., Read, R. J., Ardelt, W., Laskowski, M., Jr., & James, M. N. G. (1987) J. Mol. Biol. 195, 397-418]. Results of additional experiments performed at 15, 25, and 40 degrees C suggest that apparent ionization enthalpies for all carboxyl groups in OMTKY3 are about 0 +/- 2 kcal/mol. In the accompanying paper [Swint, L., & Robertson, A. D. (1995) Biochemistry 34, 4724-4732], the pH dependence of OMTKY3 stability is described and compared to expectations based on the pKa values described herein.

Amides↗
PubMed1995

Hydrogen bonds and the pH dependence of ovomucoid third domain stability.

Thermal denaturation of turkey ovomucoid third domain (OMTKY3) has been monitored with differential scanning calorimetry (DSC) and circular dichroism in H2O and D2O, pH 1.5 to 5 and ionic strength 0.01 to 0.71. Results from DSC experiments are in good agreement with spectroscopic studies [Swint, L., & Robertson, A.D. (1993) Protein Sci. 2, 2037-2049] and fit well to the two-state unfolding model. The average ratio of calorimetric to van't Hoff enthalpies is 0.99 +/- 0.03 (n = 16), and the average value of delta Cp is 620 +/- 20 cal/(mol K) (n = 7). The free energy of unfolding (delta G(u)o) increases in the presence of salt at both pH 1.5 and 4.5. This stabilization is not due to ion binding and probably results from screened repulsive interactions between the cationic groups of OMTKY3. At very low ionic strength, the change in delta G(u)o from pH 1.5 to 4.5, delta delta GpHo, is 3.5 +/- 0.2 kcal/mol. Few interactions between ionizing groups are affected by the addition of 200 mM KCl; delta delta GpHo decreases by only 0.4 +/- 0.3 kcal/mol. Comparison of delta delta GpHo with values calculated from the pKas of all six carboxyl groups in OMTKY3 [Schaller, W.S., & Robertson, A.D. (1995) Biochemistry 34, 4714-4723] suggests that some pKas in the denatured state may be lower than those of model compounds. Moreover, calculated values of delta delta GpHo are very sensitive to modest changes in the cooperativity of proton binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Zinc supplementation during lactation: effects on maternal status and milk zinc concentrations.

The effects of a zinc supplement on maternal zinc status and milk zinc concentrations through > or = 7 mo of lactation were examined. Seventy-one lactating women received either a daily 15-mg zinc supplement (ZS, n = 40) or placebo (NZS, n = 31) started by 2 wk postpartum in a double-blind, randomized design. Overall mean zinc intakes were 13.0 +/- 3.4 mg/d for the NZS group and 25.7 +/- 3.9 mg/d (including supplement) for the ZS group. Plasma zinc concentrations of the ZS group were significantly higher than those of the NZS group (P = 0.05). Milk zinc concentrations declined significantly over the course of the study for all subjects but were not affected by zinc supplementation. The mean dietary zinc intake observed in the nonsupplemented group was adequate to maintain normal maternal zinc status and milk zinc concentrations through > or = 7 mo lactation. Similar controlled intervention trials in less well-nourished populations will be required to assess the impact of lower zinc intakes on milk zinc concentrations.

Adult↗
PubMed1994

Solution structure of turkey ovomucoid third domain as determined from nuclear magnetic resonance data.

The solution structure of the 56 amino acid residue turkey ovomucoid third domain was determined by n.m.r. methods. Of the 661 distance constraints used in the calculations, 120 were determined by quadratic approximation of the cross-relaxation rates. The remaining constraints were crudely estimated from a more standard analysis of NOESY spectra. Additionally, 29 torsion angle constraints, 17 hydrogen bonds, and three disulfide bridges were used in the structure calculations. Stereospecific assignments were accomplished for 24 beta-methylene groups and six isopropyl methyl groups (43% chiral assignments). The addition of more accurate distance constraints to the distance geometry/simulated annealing approach resulted in a significant reduction in the dispersion of calculated backbone torsion angles and root-mean-square deviations between structures. Detailed comparisons have been made between the n.m.r. structures of OMTKY3 and published X-ray structures of the same protein and of closely related avian ovomucoid third domains. The refinement with more accurate distance constraints reduced differences between families of the n.m.r. and the X-ray structures.

Amino Acids↗
PubMed1994

Growth and intakes of energy and zinc in infants fed human milk.

The objectives of this study were to examine the growth pattern of healthy infants who were fed human milk exclusively for > or = 5 months and its relationship to intakes of milk, energy, and zinc. Monthly anthropometric measurements were obtained on 71 infants through 7 months of age and on 43 through 9 months. Milk zinc concentrations were determined and milk intake was measured by 3-day test weighing. Mean (+/- SD) calculated energy intake from human milk was 106 +/- 20, 79 +/- 11, 70 +/- 10, and 57 +/- 12 kcal/kg per day at 2 weeks and 3, 5, and 7 months of age, respectively; intake from milk plus solids was 70 +/- 13 kcal/kg at 7 months. Zinc intakes from human milk were 2.3 +/- 0.68, 1.0 +/- 0.43, 0.81 +/- 0.42, and 0.52 +/- 0.31 mg/day at these points. The maximum mean weight-for-age percentile for both sexes was 62 at 2 months; the mean percentile declined to 33 by 7 months and to 25 by 9 months of age. Mean length-for-age percentile declined from 43 at 2 weeks of age to 28 and 26 by 7 and 9 months of age, respectively. Energy intake at 2 weeks of age was positively associated with the weight increment from 2 weeks to 7 months of age (p = 0.003) and with a change in weight-for-age z scores from 2 weeks to 3 months of age (p = 0.028). Mean energy intakes of healthy breast-fed infants are lower through the first 7 months of life than current recommendations. Zinc intakes of breast-fed infants are likely to be adequate, on average, through 5 months of breast-feeding but subsequently are marginal without the introduction of weaning foods. Revision of standards for growth based on observations in breast-fed infants may be appropriate, but the possibility of growth-limiting nutrient deficiencies should also be investigated.

Body Height↗
PubMed1994

Predictors of device activation for ventricular arrhythmias and survival in patients with implantable pacemakers/defibrillators. CADENCE Investigators.

Predictors of survival and arrhythmia recurrence for patients with implanted defibrillators have been reported but patients with sustained, well-tolerated ventricular tachycardia were often excluded from these trials. Arrhythmia recurrence and survival in populations including these patients have been less well studied. The purpose of the present study was to examine predictors of spontaneous ventricular arrhythmias and mortality in patients who received a tiered therapy antitachycardia pacemaker/defibrillator for ventricular tachycardia, fibrillation, or both. Three hundred thirty-seven patients who received a Ventritex CADENCE tiered therapy antitachycardia device at one of 19 participating centers between July 11, 1989 and March 4, 1991 are included in this retrospective analysis. Diagnostic summary data and stored electrograms telemetered from the implanted device were assessed to determine characteristics of recurrent arrhythmias. Mean follow-up was 360 +/- 10 (SEM) days. Thirty-three patients died during follow-up. At least one recurrent ventricular arrhythmia was observed in 205 patients (61%). A total of 7,539 episodes were observed with a mean of 37 +/- 5 per patient. Patients with recurrent ventricular arrhythmias were slightly but significantly older (64 +/- 0.7 vs 59 +/- 1.2 years; P < 0.001) but were not distinguished by gender or underlying structural disease. Patients whose presenting arrhythmia was monomorphic ventricular tachycardia were more likely to experience recurrent ventricular arrhythmias (69% recurrence rate) than patients presenting with ventricular fibrillation or polymorphic ventricular tachycardia (46% recurrence rate; P < 0.001). Cycle length of spontaneous tachycardia was also a predictor of arrhythmia recurrence. Patients having slower ventricular arrhythmias were less likely to remain recurrence free. Mean left ventricular ejection fraction was similar for patients with and without recurrences. Younger age and absence of arrhythmia recurrence but not presenting arrhythmia were predictors of survival. We conclude that age and presentation with monomorphic ventricular tachycardia are important predictors of arrhythmia recurrence for this patient population. Exclusion of patients with monomorphic ventricular tachycardia underestimates the rate of recurrent ventricular arrhythmias and utilization of device therapy.

Adolescent↗
PubMed1994

Prevalence and determinants of elevated plasma norepinephrine concentration in compensated cirrhosis.

OBJECTIVES: Elevation of plasma norepinephrine concentration in patients with cirrhosis and ascites is attributed to sympathetic activation due to arterial underfilling. Plasma norepinephrine should thus be normal in patients without sodium retention. We examined the prevalence and determinants of elevated plasma norepinephrine concentration in compensated cirrhosis. METHODS: Forty-six studies were performed on 37 patients; nine were studied twice. Between studies, elevated plasma norepinephrine concentration fell to normal in eight patients. Standard clinical and laboratory methods were used for all measurements. RESULTS: Plasma norepinephrine was elevated (> 1.89 nmol/L) in 31 studies. Patients with normal and elevated values were similar with respect to arterial pressure, cardiac output, systemic resistance, heart rate, plasma renin activity, and plasma atrial natriuretic factor concentration. Liver function, as indicated by plasma clearance of cholic acid, antipyrine, and caffeine, was similar in the two groups, but patients with elevated norepinephrine concentration had significantly increased plasma caffeine concentrations. Plasma norepinephrine concentration significantly correlated with plasma caffeine concentration but not with any hemodynamic or neurohormonal variables. Arterial pressure fell in repeatedly studied patients in whom plasma norepinephrine concentration declined. Moreover, the changes in arterial pressure and plasma norepinephrine concentration were significantly, directly correlated. CONCLUSIONS: Sympathetic activation is common in "compensated" cirrhosis. This is not because of arterial underfilling. Indeed, blood pressure and norepinephrine concentration maintained a normal physiological relationship in repeatedly studied patients. Elevated plasma caffeine concentration as a consequence of impaired hepatic metabolic function may contribute to sympathetic activation in some patients.

Caffeine↗
PubMed1994

Antinuclear antibodies and breast implants.

Anecdotal reports have linked silicone breast implants to autoimmune diseases, with scleroderma being mentioned most often. In view of other environmental influences--such as silica mining and the toxic oil syndrome--thought to predispose to scleroderma, more systematic immunologic information on women with silicone implants is needed to assess any possible relation to autoimmunity. A cross-sectional survey was carried out with 150 women, of whom 131 had implants. Group 0 consisted of 19 volunteer women without breast implants who felt healthy, group I was 38 volunteer women with breast implants who felt healthy, group II was 82 women with implants who had various symptoms, and group III was 11 women with implants who had autoimmune disease. Scleroderma was overrepresented in group III (6 of 11). Antinuclear antibodies were determined on Hep-2 cells, using serum dilutions of 1:16, 1:64, and 1:256. A positive test was indicated by 1+ or more fluorescence at 1:256. Antinuclear antibody tests were positive in 0% of group 0, 18% of group I (P < .05 versus group 0), 26% of group II, and 64% of group III. There was no correlation between antinuclear antibody positivity and type of implant, indication for implantation, time since first implantation, total number of implants, and report of implant leak or rupture. Women with breast implants may be at risk for the development of antinuclear antibodies. Proof of such an association will require large-scale prospective studies and epidemiologic analyses.

Analysis of Variance↗
PubMed1994

Sodium retention does not occur at a critical threshold of liver function in alcoholic cirrhosis.

Sodium retention is triggered in rats with experimental liver injury at a critical threshold of liver function. We compared liver function and sodium retention in serially studied patients with alcoholic cirrhosis to determine whether a similar threshold exists in human beings. Antipyrine, caffeine, and cholic acid clearance were measured in 35 men with alcoholic liver disease. Nineteen patients were evaluated on two or more occasions; between studies, 28 remained in sodium balance (group NN), six spontaneously developed sodium retention and ascites formation (group NY), and seven spontaneously lost ascites (group YN). A threshold between patients with and without sodium retention did not exist for any of the clearance measurements. Indeed, values overlapped widely between the two groups. Antipyrine and cholate clearance were significantly reduced in patients with sodium retention, but caffeine clearance was similar in the two groups. Antipyrine and caffeine clearance declined significantly between the first and second study in group NY; cholate clearance did not change. No significant differences were observed between studies in group YN. In several patients of this group, liver function worsened as ascites spontaneously resolved. Impaired liver function commonly but not invariably accompanies sodium retention in patients with cirrhosis. A threshold at which sodium retention occurs or resolves does not exist.

Antipyrine↗
PubMed1993

Thermodynamics of unfolding for turkey ovomucoid third domain: thermal and chemical denaturation.

We have used thermal and chemical denaturation to characterize the thermodynamics of unfolding for turkey ovomucoid third domain (OMTKY3). Thermal denaturation was monitored spectroscopically at a number of wave-lengths and data were subjected to van't Hoff analysis; at pH 2.0, the midpoint of denaturation (Tm) occurs at 58.6 +/- 0.4 degrees C and the enthalpy of unfolding at this temperature (delta Hm) is 40.8 +/- 0.3 kcal/mol. When Tm was perturbed by varying pH and denaturant concentration, the resulting plots of delta Hm versus Tm yield a mean value of 590 +/- 120 cal/(mol.K) for the change in heat capacity upon unfolding (delta Cp). A global fit of the same data to an equation that includes the temperature dependence for the enthalpy of unfolding yielded a value of 640 +/- 110 cal/(mol.K). We also performed a variation of the linear extrapolation method described by Pace and Laurents, which is an independent method for determining delta Cp (Pace, C.N. & Laurents, D., 1989, Biochemistry 28, 2520-2525). First, OMTKY3 was thermally denatured in the presence of a variety of denaturant concentrations. Linear extrapolations were then made from isothermal slices through the transition region of the denaturation curves. When extrapolated free energies of unfolding (delta Gu) were plotted versus temperature, the resulting curve appeared linear; therefore, delta Cp could not be determined. However, the data for delta Gu versus denaturant concentration are linear over an extraordinarily wide range of concentrations. Moreover, extrapolated values of delta Gu in urea are identical to values measured directly.

Animals↗