Temperature Unmasks Allosteric Propensity in a Thermophilic Malate Dehydrogenase via Dewetting and Collapse.

In this work, we combine experiments and molecular simulations to unveil the hidden allosteric propensity of a thermophilic malate dehydrogenase protein (MDH). We provide evidence that, at its working temperature, the nonallosteric MDH takes a compact structure because of internal dewetting and reorganizes the active state toward functional conformations similar to its homologous allosteric LDHs. Moreover, a single-point mutation confers on the MDH a cooperative behavior that mimics an allosteric LDH. Our work not only demonstrates that thermophilic MDHs use temperature as an external parameter to regulate its functionality in a similar way allosteric LDHs use substrates/cofactors binding but also shows that the scaffold of MDHs possesses an intrinsic and hidden allosteric potentiality.

Neutron scattering observation of quasi-free rotations of water confined in carbon nanotubes.

The translational and orientational dynamics of water in carbon nanotubes has been studied by quasi-elastic neutron scattering from 300 down to 10 K. Results show that, reducing temperature below 200 K, part of this water behaves as a quasi-free rotor, that is, the orientational energy of such molecules becomes comparable to the rotational energy of water in the gas phase. This novel and unique dynamic behavior is related to the appearance of water molecules characterized by a coordination number of about two, which is promoted by sub-nanometer axial confinement. This peculiar molecular arrangement allows water to show an active rotational dynamics even at temperatures as low as 10 K. The translational mobility shows a behavior compatible with the rotational one.

Liquid 1-propanol studied by neutron scattering, near-infrared, and dielectric spectroscopy.

Liquid monohydroxy alcohols exhibit unusual dynamics related to their hydrogen bonding induced structures. The connection between structure and dynamics is studied for liquid 1-propanol using quasi-elastic neutron scattering, combining time-of-flight and neutron spin-echo techniques, with a focus on the dynamics at length scales corresponding to the main peak and the pre-peak of the structure factor. At the main peak, the structural relaxation times are probed. These correspond well to mechanical relaxation times calculated from literature data. At the pre-peak, corresponding to length scales related to H-bonded structures, the relaxation times are almost an order of magnitude longer. According to previous work [C. Gainaru, R. Meier, S. Schildmann, C. Lederle, W. Hiller, E. Rössler, and R. Böhmer, Phys. Rev. Lett. 105, 258303 (2010)] this time scale difference is connected to the average size of H-bonded clusters. The relation between the relaxation times from neutron scattering and those determined from dielectric spectroscopy is discussed on the basis of broad-band permittivity data of 1-propanol. Moreover, in 1-propanol the dielectric relaxation strength as well as the near-infrared absorbance reveal anomalous behavior below ambient temperature. A corresponding feature could not be found in the polyalcohols propylene glycol and glycerol.

Density depletion at solid-liquid interfaces: a neutron reflectivity study.

Neutron reflectivity experiments conducted on self-assembled monolayers (SAMs) against polar (water) and nonpolar (organic) liquid phases reveal further evidence for a density reduction at hydrophobic-hydrophilic interfaces. The density depletion is found at the interface between hydrophobic dodecanethiol (C12) and hexadecanethiol (C16) SAMs and water and also between hydrophilic SAMs (C12/C11OH) and nonpolar fluids. The results show that the density deficit of a fluid in the boundary layer is not unique to aqueous solid-liquid interfaces but is more general and correlated with the affinity of the liquid to the solid surface. In water the variation of pH has only minor influence, while different electrolytes taken from the Hofmeister series seem to increase the depletion. On hydrophobic SAMs an increase in density depletion with temperature was observed, in agreement with Monte Carlo simulations performed on corresponding model systems. The increase in the water density depletion layer is governed by two effects: the surface energy difference between water and the substrate and the chemical potential of the aqueous phase.

Water at solid surfaces: A review of selected theoretical aspects and experiments on the subject.

This review summarizes select aspects of the research on solid/water interfaces. Despite the considerable amount of work, the way water molecules are organized at the interface is still a source of debate. Theoretical efforts will be presented in combination with the results of computer simulations. The current status of investigations obtained with x-rays and neutron reflectometries, and sum frequency generation spectroscopy (all sensitive to the properties of solid/liquid interfaces) will be summarized and discussed.

Shear and longitudinal viscosity of non-ionic C12E8 aqueous solutions.

We present an extensive set of measurements of steady shear viscosity (eta degrees(s)), longitudinal elastic modulus (M'), and ultrasonic absorption (alpha) in the one-phase isotropic liquid region of the non-ionic surfactant C12E8 aqueous solutions. Within a given temperature interval, this phase extends along the entire surfactant concentration range that could be fully covered in the experiments. In agreement with previous studies, the overall results support the presence of two separated intervals of concentration corresponding to different structural properties. In the surfactant-rich region the temperature dependence of eta degrees(s) follows an equation characteristic of glass-like systems. The ultrasonic absorption spectra show unambiguous evidence of viscoelastic behavior that can be described by a Cole-Cole relaxation formula. In this region, when both the absorption and the frequency are scaled by the static shear viscosity (eta degrees(s)), the scaled attenuation reduces to a single universal curve for all temperatures and concentrations. In the water-rich region the behavior of eta degrees(s), M', and alpha are more complex and reflect the presence of dispersed aggregates whose size increases with temperature and concentration. At these concentrations the ultrasonic spectra are characterized by a multiple decay rate. The high-frequency tail falls in the same frequency range seen at high surfactant content and exhibits similar behaviors. This contribution is ascribed to the mixture of hydrophilic terminations and water present at the micellar interfaces that resembles the condition of a concentrated polymer solution. An additional low-frequency contribution is also observed, which is ascribed to the exchange of water molecules and/or surfactant monomers between the aggregates and the bulk solvent region.

One-day therapy for treatment of Helicobacter pylori infection.

The present study evaluated the effect of a one-day high-dose combined therapy on Helicobacter pylori infection. Thirty-two consecutive patients (suffering from either peptic ulcer or nonulcer dyspepsia) with Helicobacter pylori infection received omeprazole (40 mg) + bismuth subcitrate (240 mg x 4) + amoxicillin suspension (2000 mg x 4) + metronidazole (500 mg x 4), for only one day. Endoscopy, histology, culture, and susceptibility studies were done at entry and 30 and 90 days after the treatment day. Successful eradication was obtained in 23/32 (72%) patients and gastritis had resolved in 95% of these. Side effects were induced by the treatment in 6/32 (19%) patients, but these were all self-limiting, short-lasting, and did not require any specific treatment. Development of bacterial resistance to metronidazole occurred in 6/9 (67%) non-eradicated patients. These data suggest that one-day treatment with high doses of amoxicillin, metronidazole, bismuth, and omeprazole represents an effective, safe, and inexpensive therapeutic approach for the treatment of H. pylori infection.

Evaluation of Helicobacter pylori sensitivity to amoxycillin and metronidazole in dyspeptic patients.

We evaluated the "in vitro" sensitivity to amoxycillin and metronidazole of 193 Helicobacter pylori strains isolated from the gastric mucosa of dyspeptic patients. Susceptibility was determined by disc diffusion on agar plates. All the isolates were found to be sensitive to amoxycillin. On the contrary, 12% of the strains isolated from patients never treated for Helicobacter pylori infection and 73% of those isolated from patients who had previously received unsuccessful treatment for Helicobacter pylori infection were found to be resistant to metronidazole. Resistance was more common in women (17%) than in men (4%: p < 0.01) and was not correlated with age. The occurrence of Helicobacter pylori resistance to metronidazole is relatively common in Italy. In vitro testing of Helicobacter pylori sensitivity seems to be important before embarking on treatments aimed at eradicating the bacterium.

Fasting and postprandial gastrointestinal motility in ulcer and non-ulcer dyspepsia.

This study aimed to compare fasting and postprandial gastrointestinal motor patterns in patients with ulcer and non-ulcer dyspepsia. Forty five subjects were studied: 10 with uncomplicated gastric ulcer, eight with uncomplicated duodenal ulcer, 18 with chronic idiopathic dyspepsia, and nine healthy asymptomatic controls. Gastrointestinal fasting and postprandial motor patterns were recorded using a low compliance perfusion technique. The interdigestive antral cumulative motility index, computed for 30 minutes before the appearance of duodenal activity fronts, and the number of activity fronts with an antral component were significantly less in patients with ulcers and those with non-ulcer dyspepsia compared with asymptomatic controls. The patient groups also had a reduced antral motor response to a solid-liquid test meal compared with healthy controls. Intestinal motor abnormalities (bursts of non-propagated phasic pressure activity and discrete clustered contractions) were recorded in a minority of patients, all with associated irritable bowel symptoms. In conclusion, antral hypomotility is a frequent but nonspecific motor abnormality in dyspepsia; abnormal motor patterns of the small bowel are less frequent and seem to be confined to patients with concomitant irritable bowel syndrome.

Reversibility of gastrointestinal motor abnormalities in chronic intestinal pseudo-obstruction.

A 43-year-old man with chronic intestinal pseudo-obstruction is presented. He had undergone two laparotomies in an attempt to eliminate the cause of repeated episodes suggestive of obstruction. Gastrointestinal manometry showed severe abnormalities compatible with the diagnosis of chronic intestinal pseudo-obstruction. Laboratory tests indicated the presence of intestinal malabsorption and villous atrophy. A gluten-free diet accompanied by 10 days of treatment with tetracycline and 2 short periods of treatment with cisapride led to gradual, but apparently complete, resolution of the pseudo-obstructive syndrome. Repeated manometric studies showed progressive normalization of both the fasting and postprandial upper gastrointestinal motor pattern.

[Comparison of methods: gastro-duodenal manometry and study of gastric emptying]. / Confronto tra metodiche: manometria gastroduodenale e studio dello svuotamento gastrico.

Traditionally, the stomach is regarded as two functional unit regions: 1) a proximal portion mainly involved in receptive relaxation and emptying of liquids; and 2) a distal portion that grinds, mixes and empties solids. Manometric and radioisotopic studies have been employed to construct such a physiological model. More recently, ad hoc designed studies have led to the identification of other factors that contribute to the regulation of gastric emptying. Antral, intestinal and pyloric motility, fundic tone and antropyloroduodenal coordination appear to be all involved in the regulation of gastric emptying. Nowadays, no single technique can simultaneously measure those parameters. Gastroduodenal manometry can be regarded as the most advanced technique, in studying gastrointestinal motility. Nevertheless, fundic tone, which is an important determinant of gastric emptying, cannot be concurrently recorded.

Inhibition of gastric acid secretion and therapeutic results: is there any correlation?

The development of effective antisecretory drugs has risen the question of what is the ideal inhibition of gastric acid secretion in the treatment of peptic ulcer. Cimetidine, unlike the more recent H2-blockers and proton pump inhibitors, exerts antisecretory effects that are correlated to the blood levels of the drug. For this reason, therapeutic posologies were initially based on the pharmacokinetic features of the drug, while, more recently, direct measurement of intragastric acidity have assumed great relevance. Despite extensive research, the ideal level of gastric acid inhibition in the treatment of peptic ulcer has not been established. Greater healing rates are achieved by more potent antisecretory drugs and the duration of treatment appears to be also important, particularly to the healing of gastric ulcers. Whether the course of peptic ulcer disease is affected by the potency of the drug employed in the treatment of acute episodes has not been established.

Effects of short- and long-term administrations of famotidine and ranitidine on some pituitary, sexual and thyroid hormones.

The endocrine effects of short-term (4 weeks) and long-term (6 months) oral administration of famotidine (40 and 20 mg nocte, respectively) and ranitidine (300 and 150 mg nocte, respectively), were investigated in 20 male patients with duodenal ulcers. Basal PRL, LH, FSH and TSH serum levels were evaluated and their response to specific releasing factors, and basal blood levels of some sexual (E2, P, T) and thyroid (T3, T4) hormones. None of the treatments modified basal and RH-stimulated levels of PRL, LH, FSH and TSH, nor basal levels of sexual hormones. Regarding the thyroid hormones, no effect was observed during the administration of famotidine. On the contrary, short-term treatment with ranitidine induced a significant decrease in thyroxine serum levels, while no effect was observed during maintenance treatment.