Bancroftian filariasis in an irrigation project community in southern Ghana.
(41/15056)
An epidemiological study to document the endemicity and transmission characteristics of bancroftian filariasis was conducted in an irrigation project community in southern Ghana. In a 50% random sample of the population, the prevalence of microfilaraemia was 26.4% and the geometric mean microfilarial intensity among positives was 819 microfilariae/ml of blood. Hydrocoele was found in 13.8% of the males aged > or =18 years, and 1.4% of the residents examined, all females, had tymphoedema/elephantiasis. Detailed monitoring of the microfilarial intensity in 8 individuals over a 24-h period confirmed its nocturnal periodicity with a peak at approximately 0100 hours. The most important vector was Anopheles gambiae s.l., followed by An. funestus. The abundance of these mosquitoes and their relative importance as vectors varied considerably between the wet and the dry season. Opening of the irrigation canals late in the dry season resulted in a remarkable increase in the population of An. gambiae (8.3% of which carried infective filarial larvae) to levels comparable to those seen during the wet season, suggesting that the irrigation project is responsible for increased transmission of lymphatic filariasis in the community. (+info)
Underreporting of habitual food intake is explained by undereating in highly motivated lean women.
(42/15056)
Underreporting of habitual food intake can be explained by underrecording and/or undereating. This study was designed to discriminate between the two errors mentioned, by measuring energy and water balance. Twenty-four lean female dieticians were recruited as subjects. Energy intake and water intake were measured for 1 wk with a weighed dietary record. Energy expenditure was estimated from measurements of resting metabolic rate, and measured physical activity with a triaxial accelerometer for movement registration. Water loss was estimated with deuterium-labeled water. Energy balance was determined by measuring the change in body mass over a nonrecording week (preceding the recording week) and over the recording week. Mean energy and water intake were 8.5 +/- 1.0 MJ/d and 2.3 +/- 0.5 L/d. The change in body mass in the nonrecording week was 0.1 +/- 0.6 kg and in the recording week -0.6 +/- 0.8 kg (paired t test; P = 0.02), indicating 16% undereating. Recorded water intake plus calculated metabolic water closely matched measured water loss (r = 0.93; P = 0.0001), which indicated a high recording precision. In conclusion, in the studied group of highly motivated lean women, there was 16% underreporting of habitual food intake, which could be explained by undereating. (+info)
Water transport by the bacterial channel alpha-hemolysin.
(43/15056)
This study is an investigation of the ability of the bacterial channel alpha-hemolysin to facilitate water permeation across biological membranes. alpha-Hemolysin channels were incorporated into rabbit erythrocyte ghosts at varying concentrations, and water permeation was induced by mixing the ghosts with hypertonic sucrose solutions. The resulting volume decrease of the ghosts was followed by time-resolved optical absorption at pH 5, 6, and 7. The average single-channel permeability coefficient of alpha-hemolysin for water ranged between 1.3x10-12 cm/s and 1.5x10-12 cm/s, depending on pH. The slightly increased single-channel permeability coefficient at lower pH-values was attributed to an increase in the effective pore size. The activation energy of water transport through the channel was low (Ea=5.4 kcal/mol), suggesting that the properties of water inside the alpha-hemolysin channel resemble those of bulk water. This conclusion was supported by calculations based on macroscopic hydrodynamic laws of laminar water flow. Using the known three-dimensional structure of the channel, the calculations accurately predicted the rate of water flow through the channel. The latter finding also indicated that water permeation data can provide a good estimate of the pore size for large channels. (+info)
Benzodiazepine localisation at the lipid-water interface: effect of membrane composition and drug chemical structure.
(44/15056)
The effect of membrane chemical composition and drug chemical structure on the localisation of several benzodiazepines (BZDs) (DZ, diazepam; CZ, clonazepam; CX, chlordiazepoxide) within model membranes was investigated. We used a spectrophotometric method presented in a previous paper (B.A. Garcia, M.A. Perillo, Biochim. Biophys. Acta 1324 (1997) 76-84) based on the study of BZD acid-base equilibrium. 'Intrinsic pK' values (pKi) were calculated according to the theory of M.S. Fernandez and P. Fromherz (J. Phys. Chem. 81 (1977) 1755-1761). Homogeneous media of known dielectric constant (dioxane 0-80% v/v in water) were used to construct a curve of DeltapKi (pKi-pKw) vs. dielectric constant (D) where DeltapKi values obtained in lipidic dispersions were interpolated. In heterogeneous media consisting of aqueous dispersions of Triton X-100 micelles we determined the relative localisation depth of BZDs according to their DTriton values (36, 37 and 62 for DZ, CX and CZ respectively) taking into account that lower D values correspond to deeper localisation. pKi determined in dispersions of dipalmitoylphosphatidylcholine (dpPC) and egg phosphatidylcholine (egg-PC) mixed multilamellar vesicles showed that, when cholesterol content increased from 0 to 20 mole%, D values decreased (from 59 to 40) in dpPC vesicles and increased (from 51 to 72) in egg-PC vesicles, indicating a tendency of BZDs to penetrate deeper into less ordered interfaces. These results should be considered to understand the non-specific pharmacological effects of BZDs as well as to evaluate the actual relevance of their pharmacological concentrations. (+info)
The individual tyrosines of proteins: their spectra may or may not differ from those in water or other solvents.
(45/15056)
The overall derivative spectrum of a protein is the sum of the individual derivative spectra just as the overall ultraviolet spectrum of a protein is the sum of its component parts. The RNase and DNA binding protein Sso7d has two tyrosines and one tryptophan. We used two mutant forms of the protein to show that the individual aromatics contribute derivative spectra that can be explained on the basis of their environments. We used mutant forms of iso-1-cytochrome c to estimate the contributions of the single tryptophan and three of the five tyrosines to the overall derivative spectrum. The tryptophan spectrum is not exceptional. The comparable tyrosine spectra are more complex. The derivative spectrum of individual tyrosines does not correspond to that expected on the basis of concentration. This is a reflection of two factors: (1) the extent to which mutations are sensed distally through the introduction and compression of packing defects; and (2) the extent to which electronic transitions of tyrosine are influenced by nearby atoms. This influence could take the form of tyrosine residing in an area where the dielectric coefficient is not uniform; it could also result from tyrosine bumping into neighboring atoms with lower frequency than it does in solution. (+info)
A mechanistic analysis of the increase in the thermal stability of proteins in aqueous carboxylic acid salt solutions.
(46/15056)
The stability of proteins is known to be affected significantly in the presence of high concentration of salts and is highly pH dependent. Extensive studies have been carried out on the stability of proteins in the presence of simple electrolytes and evaluated in terms of preferential interactions and increase in the surface tension of the medium. We have carried out an in-depth study of the effects of a series of carboxylic acid salts: ethylene diamine tetra acetate, butane tetra carboxylate, propane tricarballylate, citrate, succinate, tartarate, malonate, and gluconate on the thermal stability of five different proteins that vary in their physico-chemical properties: RNase A, cytochrome c, trypsin inhibitor, myoglobin, and lysozyme. Surface tension measurements of aqueous solutions of the salts indicate an increase in the surface tension of the medium that is very strongly correlated with the increase in the thermal stability of proteins. There is also a linear correlation of the increase in thermal stability with the number of carboxylic groups in the salt. Thermal stability has been found to increase by as much as 22 C at 1 M concentration of salt. Such a high thermal stability at identical concentrations has not been reported before. The differences in the heat capacities of denaturation, deltaCp for RNase A, deduced from the transition curves obtained in the presence of varying concentrations of GdmCl and that of carboxylic acid salts as a function of pH, indicate that the nature of the solvent medium and its interactions with the two end states of the protein control the thermodynamics of protein denaturation. Among the physico-chemical properties of proteins, there seems to be an interplay of the hydrophobic and electrostatic interactions that lead to an overall stabilizing effect. Increase in surface free energy of the solvent medium upon addition of the carboxylic acid salts appears to be the dominant factor in governing the thermal stability of proteins. (+info)
Concentration and second-gas effects in the water analogue.
(47/15056)
The water analogue provides a visual model of the process of anaesthetic exchange. In the standard version, a single pipe connects the mouth container to the lung container and the conductance of this mouth-lung pipe is proportional to alveolar ventilation. This implies that inspired and expired ventilations are equal. In fact, with high inspired concentrations of nitrous oxide, early rapid uptake of gas by solution leads to a substantial difference between inspired and expired ventilation which in turn leads to concentration and second-gas effects. It is shown that by representing inspired and expired ventilations separately, and keeping one of them constant while varying the other to compensate for rapid uptake, concentration and second-gas effects are reproduced in the water analogue. Other means of reproducing the effects are reported but we believe that the first method is the most realistic and the most appropriate for teaching. (+info)
Dissection of the structural and functional role of a conserved hydration site in RNase T1.
(48/15056)
The reoccurrence of water molecules in crystal structures of RNase T1 was investigated. Five waters were found to be invariant in RNase T1 as well as in six other related fungal RNases. The structural, dynamical, and functional characteristics of one of these conserved hydration sites (WAT1) were analyzed by protein engineering, X-ray crystallography, and (17)O and 2H nuclear magnetic relaxation dispersion (NMRD). The position of WAT1 and its surrounding hydrogen bond network are unaffected by deletions of two neighboring side chains. In the mutant Thr93Gln, the Gln93N epsilon2 nitrogen replaces WAT1 and participates in a similar hydrogen bond network involving Cys6, Asn9, Asp76, and Thr91. The ability of WAT1 to form four hydrogen bonds may explain why evolution has preserved a water molecule, rather than a side-chain atom, at the center of this intricate hydrogen bond network. Comparison of the (17)O NMRD profiles from wild-type and Thr93Gln RNase T1 yield a mean residence time of 7 ns at 27 degrees C and an orientational order parameter of 0.45. The effects of mutations around WAT1 on the kinetic parameters of RNase T1 are small but significant and probably relate to the dynamics of the active site. (+info)