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PubMed1999

Development and in vitro evaluation of buccoadhesive tablets using a new model substrate for bioadhesion measures: the eggshell membrane.

For oral delivery of antimicrobial and anti-inflammatory drug, mucoadhesive tablets based on gelatin/hydroxypropylcellulose (HPC), gelatin/hydroxypropylmethyl-cellulose (HPMC), and gelatin/sodium carboxymethylcellulose (NaCMC) at different ratios were prepared by direct compression of the mixed powders. Metronidazole and benzydamine were used as model drugs. The in vitro bioadhesive properties, evaluated by a commercial tensile tester, were significantly affected by the model substrate employed, that is, a polypropylene (PP) membrane or a biological membrane (eggshell membrane). The use of the biological substrate seemed to supply more reliable data. All studied formulations showed an erosion-diffusion mechanism of release, anomalous or non-Fickian release, in agreement with the behavior of the swellable systems.

Administration, Oral↗

PubMedDate not supplied

Nitrogen excretion and the cardiorespiratory physiology of the gulf toadfish, Opsanus beta.

Gulf toadfish, Opsanus beta, are facultatively ureotelic and can excrete the majority of their nitrogenous waste as urea. Urea excretion occurs in "pulses." The hypothesis that pulsatile urea excretion reflects sudden, transient, generalized increases in the branchial conductance was investigated by the simultaneous monitoring of cardiorespiratory variables, oxygen uptake, and whole-body urea, ammonia, and/or 3H2O effluxes. The direct monitoring of both expired branchial water and water exiting a respirometer demonstrated that urea pulses were derived from the gills. No significant changes in ventilation or cardiac frequency, oxygen uptake, or ammonia efflux were observed during natural urea pulses, refuting the hypothesis that pulsatile urea excretion reflects pulsatile increases in the generalized diffusive properties of the gill for solute transfer. An alternative model for pulsatile urea excretion postulates that the gill urea permeability is increased periodically by the insertion and/or activation of specific urea transporters into gill cell membranes. Pulsatile urea excretion was abolished by pretreatment with the cytoskeletal-disrupting agent colchicine; colchicine may block trafficking of urea transporter-containing vesicles. Exocytosis of water following the fusion of vesicles with gill cell membranes could explain the significantly elevated 3H2O efflux observed during urea pulses.

Animals↗

PubMed2002

Diffuse wavefields in cylindrical coordinates.

A diffuse wavefield is normally defined in terms of plane waves--to quote one textbook definition "plane waves are incident from all directions with equal probability and random phase." In some vibro-acoustic problems the response of a two-dimensional component such as a plate is more conveniently expressed in terms of cylindrical waves, and it is not immediately obvious what properties should be assigned to the cylindrical waves to constitute a diffuse field. It is shown here that a diffuse wavefield can be modeled as a summation of statistically independent cylindrical waves, apart from the fact that each outgoing wave of a particular order is fully correlated to an incoming wave of the same order. A simple relationship is derived between the energy flow P in each wave component and the energy density e of the wavefield: P = ec(g)/k, where c(g) is the group velocity and k is the wavenumber. This result is shown to hold true for both bending waves and in-plane waves (longitudinal and shear) in a plate. The work has application to the calculation of coupling loss factors in statistical energy analysis.

Journal Article↗

PubMed2002

Waves of larch budmoth outbreaks in the European alps.

Spatially extended population models predict complex spatiotemporal patterns, such as spiral waves and spatial chaos, as a result of the reaction-diffusion dynamics that arise from trophic interactions. However, examples of such patterns in ecological systems are scarce. We develop a quantitative technique to demonstrate the existence of waves in Central European larch budmoth (Zeiraphera diniana Gn.) outbreaks. We show that these waves travel toward the northeast-east at 210 kilometers per year. A theoretical model involving a moth-enemy interaction predicts directional waves, but only if dispersal is directionally biased or habitat productivity varies across the landscape. Our study confirms that nonlinear ecological interactions can lead to complex spatial dynamics at a regional scale.

Animals↗

PubMedDate not supplied

The use of microdialysis in pharmacokinetics and pharmacodynamics.

Microdialysis is a new in vivo sampling technology applied to the study of pharmacokinetics and drug metabolism in the blood and soft tissues of living systems. A small-diameter probe containing a dialysis membrane is implanted into tissue and perfused with a suitable fluid. Low-molecular-weight substances passively diffuse through the semipermeable membrane along a concentration gradient, resulting in the collection of purified dialysate samples. The advantage of this approach over blood sampling and dissection of tissues is the ability to sample blood and extracellular fluid with minimal tissue damage or alteration of fluid balance. Sampling several tissues simultaneously and continuously in animal models allows data to be obtained that more directly reflect interactions of drugs at their sites of activity and detoxification. Techniques such as this will have a tremendous impact on preclinical and clinical pharmacologic research.

Animals↗

PubMed2005

Neuropathologic substrate of cerebral palsy.

Animal models have assisted in understanding the mechanisms of brain injury underlying cerebral palsy. Nevertheless, no such models replicate every aspect of the human disease. This review summarizes the classic and more recent studies of the neuropathology of human perinatal brain injury most commonly associated with cerebral palsy, for use by researchers and clinicians alike who need to analyze published animal models with respect to their fidelity to the human disorder. The neuropathology underlying cerebral palsy includes white-matter injury, known as periventricular leukomalacia, as well as germinal matrix hemorrhage with intraventricular extension, and injury to the cortex, basal ganglia, and thalamus. Each has distinctive features while sharing some risk factors, such as prematurity and/or hypoxia-ischemia in the perinatal period. Periventricular leukomalacia consists of diffuse injury of deep cerebral white matter, with or without focal necrosis. Recent work directly in human postmortem tissue has focused on the role of free radical injury, cytokine toxicity (especially in light of the epidemiologic association of periventricular leukomalacia with maternofetal infection), and excitotoxicity in the development of periventricular leukomalacia. Premyelinating oligodendrocytes, which predominate in periventricular regions during the window of vulnerability to periventricular leukomalacia (24-34 postconceptional weeks), are the targets of free radical injury, as determined by immunocytochemical markers of lipid peroxidation and protein nitration. This maturational susceptibility can be attributed in part to a relative deficiency of superoxide dismutases in developing white matter. Microglia, which respond to cytokines and to bacterial products such as lipopolysaccharide via Toll-like receptors, are increased in periventricular leukomalacia white matter and can contribute to cellular damage. Indeed, several cytokines, including tumor necrosis factor-a and interleukins 2 and 6, as well as interferon-g, have been demonstrated in periventricular leukomalacia. Preliminary work suggests a role for glutamate receptors and glutamate transporters in periventricular leukomalacia based on expression in human developing oligodendrocytes. Germinal matrix hemorrhage, with or without intraventricular hemorrhage, occurs in premature infants and can coexist with periventricular leukomalacia. Studies in human germinal matrix tissue have focused on maturation-based vascular factors, such as morphometry and expression of molecules related to the structure of the blood-brain barrier. Gray-matter injury, seen more commonly in term infants, includes cortical infarcts and status marmoratus. Subtle cortical injury overlying periventricular leukomalacia is the subject of current interest as a possible substrate for the cognitive difficulties seen in patients with cerebral palsy. In summary, it is hoped that work in human tissue, in conjunction with experimental animal models, will lead to eventual therapeutic or preventive strategies for the perinatal brain injury underlying cerebral palsy.

Autopsy↗

PubMed2005

Dynamical susceptibility of glass formers: contrasting the predictions of theoretical scenarios.

We compute analytically and numerically the four-point correlation function that characterizes nontrivial cooperative dynamics in glassy systems within several models of glasses: elastoplastic deformations, mode-coupling theory (MCT), collectively rearranging regions (CRR's), diffusing defects, and kinetically constrained models (KCM's). Some features of the four-point susceptibility chi(4) (t) are expected to be universal: at short times we expect a power-law increase in time as t(4) due to ballistic motion (t(2) if the dynamics is Brownian) followed by an elastic regime (most relevant deep in the glass phase) characterized by a t or sqrt[t] growth, depending on whether phonons are propagative or diffusive. We find in both the beta and early alpha regime that chi(4) approximately t(mu), where mu is directly related to the mechanism responsible for relaxation. This regime ends when a maximum of chi(4) is reached at a time t= t(*) of the order of the relaxation time of the system. This maximum is followed by a fast decay to zero at large times. The height of the maximum also follows a power law chi(4) (t(*)) approximately t(*lambda). The value of the exponents mu and lambda allows one to distinguish between different mechanisms. For example, freely diffusing defects in d=3 lead to mu=2 and lambda=1 , whereas the CRR scenario rather predicts either mu=1 or a logarithmic behavior depending on the nature of the nucleation events and a logarithmic behavior of chi(4) (t(*)) . MCT leads to mu=b and lambda=1/gamma , where b and gamma are the standard MCT exponents. We compare our theoretical results with numerical simulations on a Lennard-Jones and a soft-sphere system. Within the limited time scales accessible to numerical simulations, we find that the exponent mu is rather small, mu<1 , with a value in reasonable agreement with the MCT predictions, but not with the prediction of simple diffusive defect models, KCM's with noncooperative defects, and CRR's. Experimental and numerical determination of chi(4) (t) for longer time scales and lower temperatures would yield highly valuable information on the glass formation mechanism.

Journal Article↗

PubMed2002

Physiological model of the stimulative effects of alcohol in low-to-moderate doses.

A physiological model of alcohol use is proposed, based on the observation that ethanol is a natural intracellular metabolite. It is suggested that ethanol synthesis is an intermediate step in the metabolic pathway of elimination of the excess of energy-releasing substrates from mitochondria and the cytosol when the cell does not require additional energy. The process is first of all important for elimination of acetyl-CoA from mitochondria. Ingested alcohol passes across plasma and mitochondrial membranes by diffusion and follows the endogenous ethanol pathway but in the reverse direction. This pathway is used when the cell needs additional energy. In that case, exogenous ethanol supplies the respiratory chain with electrons via NADH on the path of oxidation to acetaldehyde and then to acetate by alcohol and aldehyde dehydrogenases. After conversion to acetyl-CoA, it goes into the citrate cycle and is thus used for energy production entirely. If citrate cycle activity is decreased constitutionally, acetyl-CoA enters into citrate cycle too slowly and energy deficit arises, ethanol compensates for the energy deficit. Acetate then diffuses out of mitochondria. The less energy production in mitochondria, the more the cell is ready to accept alcohol as an energy source. Citrate cycle activity can be depressed as a result of single-nucleotide polymorphisms of genes controlling some enzymes involved in the cycle, which influences the alcohol requirement.

Central Nervous System Stimulants↗

PubMed2005

Migration modelling from food-contact plastics into foodstuffs as a new tool for consumer exposure estimation.

One important aspect within the European Union's public healthcare is the exposure of consumers to undesirable chemicals in the diet. Food-contact materials (FCM) are one potential contamination source and therefore of particular interest for food exposure assessment. On the other hand, scientific investigations concerning the migration potential and behaviour of food-packaging materials have demonstrated that diffusion in and migration from FCM are foreseeable physical and, in principle, mathematically describable processes. Because of this situation and the current state-of-the-art in migration science, a research project was initiated within the 5th Framework Programme of the European Commission. This project, with the acronym 'FOODMIGROSURE' (European Union Contract No. 'QLK1-CT2002-2390') started on 1 March 2003, was due to last 3 years and had the participation of nine European project partners (see the project website: www.foodmigrosure.org). The aim of the project was to extend currently existing migration models (which have been demonstrated to be applicable for less complex matrices such as food simulants) to foodstuffs themselves. In this way, the project aims to provide a novel and economic tool for estimation of consumer exposure to chemicals migrating from food-contact plastic materials under any actual contact conditions. In addition, the project aims to increase knowledge of the mechanisms of diffusion of organic compounds in foodstuffs and provide data on the partitioning effects between FCM and foods. Today the latter aspect is increasingly regarded as a fundamental influence parameter for migration into foods. Based on the project achievements, a much better scientific basis is available to allow scientifically appropriate amendments of European Union Directive 85/572/EEC as well as to support further developments with the so-called Plastics Directive 2002/72/EC. The paper introduces the project and presents an overview of the project work progress.

Attitude to Health↗

PubMed1991

The albedo and scattering phase function of interstellar dust and the diffuse background at far-ultraviolet wavelengths.

We have determined the scattering parameters of dust in the interstellar medium at far-ultraviolet (FUV) wavelengths (1415-1835 angstroms). Our results are based on spectra of the diffuse background taken with the Berkeley UVX spectrometer. The unique design of this instrument makes possible for the first time accurate determination of the background both at high Galactic latitude, where the signal is intrinsically faint, and at low Galactic latitude, where direct starlight has heretofore compromised measurements of the diffuse emission. Because the data are spectroscopic, the continuum can be distinguished from the atomic and molecular transition features which also contribute to the background. We find the continuum intensity to be well correlated with the Galactic neutral hydrogen column density until saturation at about 1200 photons cm-2 s-1 sr-1 angstrom-1 is reached where tau FUV approximately 1. Our measurement of the intensity where tau FUV > or = 1 is crucial to the determination of the scattering properties of the grains. We interpret the data with a detailed radiative transfer model and conclude that the FUV albedo of the grains is low (<25%) and that the grains scatter fairly isotropically. We evaluate models of dust composition and grain-size distribution and compare their predictions with these new results. We present evidence that, as the Galactic neutral hydrogen column density approaches zero, the FUV continuum background arises primarily from scattering by dust, which implies that dust may be present in virtually all view directions. A non-dust-scattering continuum component has also been identified, with an intensity (external to the foreground Galactic dust) of about 115 photons cm-2 s-1 angstrom-1. With about half this intensity accounted for by two-photon emission from Galactic ionized gas, we identify roughly 50 photons cm-2 s-1 sr-1 angstrom-1 as a true extragalactic component.

Astronomy↗

PubMed2002

Simulation of Ca2+ release from the sarcoplasmic reticulum with three-dimensional sarcomere model in cardiac muscle.

A simulation of some basic features of Ca(2+) release from the sarcoplasmic reticulum (SR) in cardiac muscle was made with a model based on the mechanism of Ca(2+)-induced Ca(2+)-release. The half-sarcomere modeled as a circular cylinder was divided into 20 annular elements in the radial, 50 slices in the axial, and 125 slices in the azimuthal direction. The cylindrical surface of the sarcomere was covered by a layer of the SR. The rate of Ca(2+) release from the terminal sac (TS) is proportional to the product of the open probability of the Ca(2+) release channel and the difference of [Ca(2+)] between the TS and an element facing the TS. Ca(2+) moves from element to element by simple diffusion and is taken up by the tubular SR via Ca(2+)-ATPase. Ca(2+) influx (I(ca)) to trigger the TS Ca(2+) release was introduced to either a single element facing the TS (local I(ca)) or to 20 elements aligned at the level of the Z-line (uniform I(ca)). The simulation showed that with both types of I(ca), TS Ca(2+) release is smoothly graded over a wide range of I(ca) with the TS moderately loaded with Ca(2+). The gain determined by dividing the total amount of TS Ca(2+) release by I(ca) was greater with local than with uniform I(ca). Mechanical alternans was simulated with both the local and uniform I(ca) with an appropriate rate of Ca(2+) replenishment to the TS. A Ca(2+) wave was simulated with a model consisting of 8 longitudinally consecutive sarcomeres with TS heavily loaded with Ca(2+). Thus the present model accounted for graded TS Ca(2+) release, mechanical alternans, and Ca(2+) wave in cardiac muscle at the same time.

Calcium↗

PubMed1992

Mapping of cerebral energy metabolism in rats with genetic generalized nonconvulsive epilepsy.

The quantitative 2-[14C]deoxyglucose autoradiographic method was applied to measure local cerebral metabolic rates of glucose (LCMRglc) in a model of genetic petit-mal-like seizures in a strain of Wistar rats. During the experimental period, epileptic rats exhibited synchronous spike-and-wave discharges, whereas the EEG pattern of control animals was normal. Overall, LCMRglc was consistently higher in epileptic rats than in the non-epileptic controls. The increase in LCMRglc was widespread and concerned all cerebral functional systems studied, whether they exhibit spike-and-wave discharges (neocortex and thalamus), or not (limbic system). These results are in good accordance with positron-emission tomography measurements in humans with typical childhood absence epilepsy. There appears to be a lack of anatomical correlation between areas demonstrating hypermetabolism and areas where spike-and-wave discharges are recorded. The administration of 200 mg/kg ethosuximide completely suppressed spike-and-wave discharges in epileptic rats and did not change the EEG pattern in controls. However, LCMRglc were increased to the same extent over control values in epileptic rats whether they were injected with ethosuximide or untreated. By contrast, when epileptic rats were given 2 mg/kg haloperidol, the frequency and the length of spike-and-wave discharges increased, inducing almost a permanent petit-mal status epilepticus. Haloperidol did not change EEG pattern in controls. In haloperidol-treated epileptic rats, LCMRglc decreased to levels comparable to those measured in untreated control rats. In the presence of haloperidol, LCMRglc were similar in both control and epileptic rats. Thus, the diffuse increase in cerebral energy metabolism in epileptic rats as compared to controls is not directly related to the occurrence of spike-and-wave discharges, and may rather be associated with inhibitory mechanisms involved in their termination and suppression, as well as their spread to limbic and motor structures.

Animals↗

PubMed2002

Nonequilibrium phase transitions in a model for the origin of life.

The requisites for the persistence of small colonies of self-replicating molecules living in a two-dimensional lattice are investigated analytically in the infinite diffusion or mean-field limit and through Monte Carlo simulations in the position-fixed or contact process limit. The molecules are modeled by hypercyclic replicators A that are capable of replicating via binary fission A+E-->2A with production rate s, as well as via catalytically assisted replication 2A+E-->3A with rate c. In addition, a molecule can degrade into its source materials E with rate gamma. In the asymptotic regime, the system can be characterized by the presence (active phase) and the absence (empty phase) of replicators in the lattice. In both diffusion regimes, we find that for small values of the ratio c/gamma these phases are separated by a second-order phase transition that is in the universality class of the directed percolation, while for small values of s/gamma the phase transition is of first order. Furthermore, we show the suitability of the dynamic Monte Carlo method, which is based on the analysis of the spreading behavior of a few active cells in the center of an otherwise infinite empty lattice, to address the problem of the emergence of replicators. Rather surprisingly, we show that this method allows an unambiguous identification of the order of the nonequilibrium phase transition.

Biophysical Phenomena↗

PubMed1981

The optics of human skin.

An integrated review of the transfer of optical radiation into human skin is presented, aimed at developing useful models for photomedicine. The component chromophores of epidermis and stratum corneum in general determine the attenuation of radiation in these layers, moreso than does optical scattering. Epidermal thickness and melanization are important factors for UV wavelengths less than 300 nm, whereas the attenuation of UVA (320-400 nm) and visible radiation is primarily via melanin. The selective penetration of all optical wavelengths into psoriatic skin can be maximized by application of clear lipophilic liquids, which decrease regular reflectance by a refractive-index matching mechanism. Sensitivity to wavelengths less than 320 nm can be enhanced by prolonged aqueous bathing, which extracts urocanic acid and other diffusible epidermal chromophores. Optical properties of the dermis are modelled using the Kubelka-Munk approach, and calculations of scattering and absorption coefficients are presented. This simple approach allows estimates of the penetration of radiation in vivo using noninvasive measurements of cutaneous spectral remittance (diffuse reflectance). Although the blood chromophores Hb, HbO2, and bilirubin determine dermal absorption of wavelengths longer than 320 nm, scattering by collagen fibers largely determines the depths to which these wavelengths penetrate the dermis, and profoundly modifies skin colors. An optical "window" exists between 600 and 1300 nm, which offers the possibility of treating large tissue volumes with certain long-wavelength photosensitizers. Moreover, whenever photosensitized action spectra extend across the near UV and/or visible spectrum, judicious choice of wavelengths allows some selection of the tissue layers directly affected.

Epidermis↗

PubMed1979

A simple experimental approach to the determination of carrier transport parameters for unlabeled substrate analogs.

A method is described by which affinities and transport rates for unlabeled substrate analogs are readily determined, and which is based on the effect of an unlabeled analog upon the rate of transport of a labeled substrate present at a low concentration on the trans side of the membrane. The procedure is widely applicable since it does not depend on assumptions about rrate-limiting steps and holds for both active and non-active systems. Here it is applied in an experimental study of the facilitated diffusion system for choline in erythrocytes, and it is shown that the transport parameters for a test substrate obtained by this method are the same as those found when the transport of the substrate is followed directly.

Biological Transport↗

PubMed2001

Agricultural use of organophosphate pesticides and the risk of non-Hodgkin's lymphoma among male farmers (United States).

OBJECTIVE: Data from three population-based case-control studies conducted in Kansas, Nebraska, Iowa, and Minnesota were pooled to evaluate the relationship between the use of organophosphate pesticides and non-Hodgkin's lymphoma (NHL) among white male farmers. METHODS: The data set included 748 cases of non-Hodgkin's lymphoma and 2236 population-based controls. Telephone or in-person interviews were utilized to obtain information on the use of pesticides. Odds ratios (OR) adjusted for age, state of residence, and respondent status, as well as other pesticide use where appropriate, were estimated by logistic regression. RESULTS: Use of organophosphate pesticides was associated with a statistically significant 50% increased risk of NHL, but direct interviews showed a significantly lower risk (OR = 1.2) than proxy interviews (OR = 3.0). Among direct interviews the risk of small lymphocytic lymphoma increased with diazinon use (OR = 2.8), after adjustment for other pesticide exposures. CONCLUSIONS: Although we found associations between the risk of NHL and several groupings and specific organophosphate pesticides, larger risks from proxy respondents complicate interpretation. Associations, however, between reported use of diazinon and NHL, particularly diffuse and small lymphocytic lymphoma, among subjects providing direct interviews are not easily discounted.

Adult↗

PubMed1994

Staining characteristics and antiviral activity of sulforhodamine B and lissamine green B.

PURPOSE: Fluorescein and rose bengal are dyes used routinely in the examination of the ocular surface. As part of an ongoing search for a superior ophthalmic dye with optimal specificity and sensitivity and a lack of interference with subsequent viral cultures, and as part of studies that use chemical dyes to understand better the pathophysiology of ocular surface disorders, the staining characteristics and antiviral activity of sulforhodamine B and lissamine green B were investigated. METHODS: Staining of rabbit corneal epithelial cell cultures by sulforhodamine B and lissamine green B was compared to that of fluorescein and rose bengal. Diffusion of each dye through a collagen gel was measured. Uptake of lissamine green B by herpes simplex virus type 1 (HSV-1)-infected Vero cell cultures was compared at several times postinfection. The effect of sulforhodamine B and lissamine green B on HSV-1 plaque formation in Vero cells was determined. The cellular toxicity of sulforhodamine B and lissamine green B in vitro was examined by a quantitative 14C-amino acid uptake assay and by a qualitative cell viability assay. Finally, the effect of sulforhodamine B and lissamine green B on viral replication was compared in vivo with that of rose bengal in a rabbit model of herpetic epithelial keratitis. RESULTS: Rose bengal vividly stained cell monolayers of explant cultures of rabbit corneal epithelium. By light microscopy, sulforhodamine B and lissamine green B, like fluorescein, did not stain the epithelial cells, but did stain the corneal explant stroma. Pretreatment of epithelial cells with 0.25% trypsin for 5 minutes failed to induce dye uptake; however, pretreatment with 0.5% Triton X-100 for 5 minutes resulted in nuclear staining by lissamine green B, but not sulforhodamine B. When added to a collagen gel, the relative diffusion rate was fluorescein > lissamine green B > sulforhodamine B > rose bengal. By spectrophotometric analysis, HSV-1-infected and uninfected Vero cells bound equivalent amounts of lissamine green B until late in infection, when infected cells took up more dye (P < 0.001). A direct neutralization assay showed that 0.06% lissamine green B or 0.5% sulforhodamine B reduced HSV-1 plaque formation in Vero cells by greater than 50%, when present at the time of viral adsorption. By a quantitative 14C-amino acid uptake assay, lissamine green B was toxic to Vero cells in a dose-dependent manner, whereas sulforhodamine B was relatively nontoxic at the concentrations tested. By a cell viability assay, however, neither dye showed significant cellular toxicity. In a rabbit model of herpetic epithelial keratitis, rose bengal significantly reduced viral replication and recovery, whereas sulforhodamine B and lissamine green B had no effect. CONCLUSIONS: Neither sulforhodamine B nor lissamine green B stain healthy, normal cells. Lissamine green B stains membrane-damaged epithelial cells, but sulforhodamine B does not. Both sulforhodamine B and lissamine green B stain corneal stroma. Lissamine green B inhibits HSV-1 plaque formation at low concentrations of dye in vitro, which correlates with suppression of cellular metabolism as demonstrated by a 14C-amino acid uptake assay, but does not affect cell viability. Neither sulforhodamine B nor lissamine green B inhibit viral replication or recovery in vivo.

Animals↗

PubMed1993

Gaugement of the inner space of the apomyoglobin's heme binding site by a single free diffusing proton. II. Interaction with a bulk proton.

The reaction mechanism and the dynamic aspects of protonation of a defined moiety located inside an aqueous cavity in a protein were monitored by time resolved spectroscopy using the pyranine apomyoglobin complex as a model (Shimoni, Tsfadia, Nachliel, and Gutman, 1993, Biophys. J. 64:472-479). The reaction was synchronized by a short laser pulse and the reprotonation of the ground state pyranine anion (phi O-) was monitored, in the microsecond time scale, by its transient absorption at 457 nm. The observed signal was reconstructed by a numeric solution of nonlinear, coupled differential equations which account for the direct reaction of phi O- with bulk proton and by proton transfer from the nearby amino acids: His 64, Asp 44, Asp 60, and Glu 59. A unique combination of rate constant was obtained which quantitates the contribution of each pathway to the overall relaxation process. In the first phase of the dynamics phi O- abstracts a proton from the nearby protonated histidine. The bulk proton interacts preferentially with the cluster of three carboxylates and immediately shuttled to the deprotonated histidine. The high proximity of the reactive groups and the strong electrostatic forces operating inside the heme binding cavity render the rate of proton transfer in the site ultrafast.

Animals↗