Cobinding of bilirubin and sulfonamide and of two bilirubin molecules to human serum albumin: a site model

Differential light absorption spectra of the bilirubin-albumin 1:1 complex, obtained on addition of 20 different sulfonamides, differ with respect to shape and amplitude. This finding seems to indicate that the sulfonamide molecule is bound in direct touch with the bilirubin. The light absorption spectrum of bilirubin-albumin 1:1 undergoes changes on cobinding of a fatty acid anion, laurate, and on variation of pH, previously explained by a change of dihedral angle between the two chromophores of the bilirubin molecule. In bilirubin-albumin 2:1, binding of laurate and variation of pH cause little change of the spectrum. This is best explained by binding of the two bilirubin molecules in close proximity, preventing conformational changes in the complex. From measurements of fluorescence of the lone tryptophan group in albumin and quenching on binding of bilirubin, we calculated the distance of 22 A from tryptophan to the first bound bilirubin molecule, and of 18 A to the second. Mutual quenching of the bilirubin fluorescence from two bound bilirubin molecules seemed to indicate that the two are bound closely together. A model of bilirubin-albumin with a binding site capable of accommodating one bilirubin and one sulfonamide molecule, or two molecules of bilirubin, is compatible with our findings.     

Chronic Helicobacter pylori Infection Does Not Significantly Alter the Microbiota of the Murine Stomach

We examined the impact of Helicobacter pylori infection on the murine gastric microbiota by culture and terminal-restriction fragment length polymorphism and found that neither acute nor chronic H. pylori infection substantially affected the gastric microbial composition. Interestingly, the total H. pylori burden detected by real-time PCR was significantly higher than that revealed by viable counts, suggesting that the antigenic load sustaining H. pylori-induced gastritis could be considerably higher than previously believed.     

Myristic acid binding to human serum albumin investigated by dialytic exchange rate

Dialysis rate determinations of several fatty acids in the absence of albumin revealed that the myristate anion, like that of laurate, in aqueous solution, pH 7.5, is present as a monomer anion when the concentration is below 25 microM. Palmitate and oleate solutions, on the other hand, show a tendency to aggregation even at concentrations below 0.5 microM. Multiple binding of myristate to human serum albumin in phosphate buffer, at pH 7.5, 37 degrees C, was investigated by exchange of 14C-labeled myristate across a dialysis membrane under conditions of binding equilibrium. A binding isotherm was established by least squares fitting of the stoichiometric binding constants in the stepwise binding equation to the experimental data. The best-fit solution was supplemented with 30 acceptable solutions within a probability limit of 0.95. A concept of one or two distinct high-affinity sites for binding of fatty acids could not be verified; the observations allow a variety of binding mechanisms ranging from cooperativity of the first two myristates to a model with four equal and independent sites.     

Acorn mast drives long-term dynamics of rodent and songbird populations

Resource pulses can have cascading effects on the dynamics of multiple trophic levels. Acorn mast is a pulsed resource in oak-dominated forests that has significant direct effects on acorn predators and indirect effects on their predators, prey, and pathogens. We evaluated changes in acorn mast, rodent abundance, raptor abundance, and reproductive success of a ground-nesting songbird over a 24-year period (1980–2004) in the southern Appalachian Mountains in an effort to determine the relationships among the four trophic levels. In particular, we examined the following: acorn mast from red oaks (Quercus rubra) and white oaks (Q. alba), abundance of white-footed mice (Peromyscus leucopus) and deer mice (P. maniculatus), population estimates of seven raptor species from three feeding guilds, and nest failure and number of juveniles of dark-eyed juncos (Junco hyemalis). Finally, we recorded seasonal temperature and precipitation to determine the effects of weather on each trophic level. We found that weather patterns had delayed effects of up to 3 years on these trophic interactions. Variation in acorn mast, the keystone resource in this community, was explained by weather conditions as far back as 2 years before the mast event. Acorn mast, in turn, was a strongly positive predictor of rodent abundance the following year, whereas spring and summer temperature and raptor abundance negatively affected rodent abundance. Dark-eyed junco nests were more likely to fail in years in which there were more rodents and raptors. Nest failure rate was a strong predictor of the number of juvenile juncos caught at the end of the summer. Our results improve our understanding of the complex ecological interactions in oak-dominated forests by illustrating the importance of abiotic and biotic factors at different trophic levels. Ethan D. Clotfelter and Amy B. Pedersen contributed equally to the writing of this paper.     

Pathogenicity of Vibrio anguillarum serogroup O1 strains compared to plasmids,outer membrane protein profiles and siderophore production

The virulence of 18 strains of Vibrio anguillarum serogroup O1 was compared to plasmid content, expression of siderophores and outer membrane proteins. All strains, irrespective of plasmid content, produced siderophores and inducible outer membrane proteins under iron-limited conditions. Only strains that carried the 67 kbp virulence plasmid or derivatives of it produced the outer membrane protein, OM2. All virulent strains harboured the 67 kbp plasmid or derivatives of it, indicating its importance for virulence. However, some strains carrying the virulence plasmid or a derivative of it, produced siderophores as well as OM2 but were non-pathogenic to fish. Likewise, among the virulent strains, considerable variation in LD50 values was recorded. Plasmid profiling and restriction analysis showed that the virulence plasmid existed in various molecular weights from 26 to 80 kbp, with 65-67 kbp being the most common, and that this plasmid displayed various restriction profiles. The presence of other plasmids did not seem to affect the pathogenic properties.     

Association between Body Mass Index,Asymmetric Dimethylarginine and Risk of Cardiovascular Events and Mortality in Norwegian Patients with Suspected Stable Angina Pectoris

Background

Asymmetric dimethylarginine (ADMA) is associated with increased risk of atherosclerotic cardiovascular disease and mortality through inhibition of nitrogen oxide (NO) synthesis. As positive correlations between serum concentrations of NO and body mass index (BMI) have been observed, we aimed to explore whether the potential associations between plasma ADMA levels and the risk of acute myocardial infarction (AMI) and mortality were modified by BMI.

Methods

Multivariable Cox proportional hazard models were used to estimate the hazard ratios (HR) for AMI, cardiovascular death and all-cause mortality according to baseline plasma ADMA levels in 4122 patients with suspected stable angina pectoris. Analyses were subsequently repeated in patients with BMI below (low BMI) or above (high BMI) median.

Results

A total of 2982 patients (72%) were men. Median (range) age, plasma ADMA level and BMI were 62 (21–88) years, 0.54 (0.10–1.25) μmol/L and 26.3 (18.5–54.3) kg/m², respectively. During a mean (standard deviation) follow-up time of 4.7 (1.4) years, 337 (8%) patients suffered from an AMI, 300 (7%) died, whereof 165 (55%) due to cardiovascular disease. Each 0.1 μmol/L increment in plasma ADMA level was associated with an increased risk of AMI (HR (95% CI) 1.21 (1.08, 1.35) and cardiovascular death 1.30 (1.13, 1.49) in participants with low BMI only. Interactions were significant for AMI (p = 0.04) and CV death (p = 0.03). BMI did not modify the association between plasma ADMA levels and all-cause mortality.

Conclusion

Plasma ADMA levels were associated with risk of AMI and cardiovascular death among patients with low BMI only.     

Interactive effects of intracisternal oxytocin and other centrally active substances on colonic temperatures of mice

Oxytocin (OXY) administered intracisternally to adult male mice produced a significant dose-related (1-4 micrograms) increase in colonic temperatures at an ambient temperature of 25 degrees C. The maximal rise in temperature occurred 30 min after administration of the peptide. The interactive effects on colonic temperature of central OXY with equimolar amounts of neurotensin, bombesin or beta-endorphin or of 2 2 mg/kg of chlorpromazine were investigated. OXY significantly antagonized the hypothermia produced by all of these substances. Pretreatment of mice with haloperidol or naloxone failed to prevent OXY-induced hyperthermia. The hyperthermic action of OXY and the interactive effects of OXY with other peptides on thermoregulation may be physiologically significant during parturition and lactation.     

Relative spectral response as a function of sequential ligand binding

A unique method is presented for the determination of the critical number of ligands that must bind to a macromolecule to elicit a spectroscopic response. This method is based on analysis of ligand binding data. For example, four Ca2+ and two Mg2+ ions are necessary for mirroring the relative decrease in the intrinsic fluorescence of bovine prothrombin fragment 1. For application of the method, ligand loading and relative spectroscopic response data must be measured over a full range of concentrations.     

Occurrence of VIP and peptide HM in human pancreas and their influence on pancreatic endocrine secretion in man

By immunohistochemistry it was found that VIP- and peptide HI/peptide HM (PHI/PHM)-like immunoreactivity occurred in autonomic neurons in the human pancreas. Antisera against both VIP and PHI/PHM reacted with neuronal cells in local ganglia and these ganglia also contained PHI/PHM- and VIP-immunoreactive fibre plexuses. VIP- and PHI/PHM-positive fibres were also seen close to the Langerhans' islets. In addition, PHI/PHM- but not VIP-like immunoreactivity was observed in the endocrine cells often located in the periphery of the islets. The nature of these PHI/PHM-positive cells remains to be established. I.v. infusion of VIP at constant rates of 300 and 900 pmol/kg X h for 30 min in 6 healthy volunteers resulted in plateau values of 102 +/- 26 and 291 +/- 25 pM, respectively. These levels of VIP which are above those found in the circulation under physiological conditions stimulated secretion of insulin, C-peptide and pancreatic glucagon dose-dependently. On the contrary prolonged (60 min) infusion of PHM in doses resulting in plasma levels up to 1340 +/- 405 pM had no effect on pancreatic hormone secretion. These findings suggest that VIP is a likely neurotransmitter in the control of endocrine pancreatic secretion while PHM has a less prominent role, if any.