Hydration and protein folding in water and in reverse micelles: compressibility and volume changes.
The partial specific volume and adiabatic compressibility of proteins reflect the hydration properties of the solvent-exposed protein surface, as well as changes in conformational states. Reverse micelles, or water-in-oil microemulsions, are protein-sized, optically-clear microassemblies in which hydration can be experimentally controlled. We explore, by densimetry and ultrasound velocimetry, three basic proteins: cytochrome c, lysozyme, and myelin basic protein in reverse micelles made of sodium bis (2-ethylhexyl) sulfosuccinate, water, and isooctane and in aqueous solvents. For comparison, we use beta-lactoglobulin (pI = 5.1) as a reference protein. We examine the partial specific volume and adiabatic compressibility of the proteins at increasing levels of micellar hydration. For the lowest water content compatible with complete solubilization, all proteins display their highest compressibility values, independent of their amino acid sequence and charge. These values lie within the range of empirical intrinsic protein compressibility estimates. In addition, we obtain volumetric data for the transition of myelin basic protein from its initially unfolded state in water free of denaturants, to a folded, compact conformation within the water-controlled microenvironment of reverse micelles. These results disclose yet another aspect of the protein structural properties observed in membrane-mimetic molecular assemblies. (+info)
Increasing peritoneal contact area during dialysis improves mass transfer.
Previous studies in mice demonstrated that relatively large volumes in the peritoneal cavity made contact with only 40% of the anatomic peritoneum and that this contact area (A(contact)) could be increased with use of a surfactant, dioctyl sodium sulfosuccinate (DSS). To investigate the hypothesis that mass transfer rates during peritoneal dialysis are dependent on the area of peritoneum in contact with the dialysis solution, rats were dialyzed for 2 h with a solution that contained (14)C-mannitol, with or without 0.02% DSS. The mass transfer-area coefficients (MTAC) were determined to be (mean +/- SEM, ml/min): no DSS, 0.163 +/- 0.008; with DSS, 0.247 +/- 0.006 (P < 0.002). DSS also caused an increase in total protein loss over 2 h (mean +/- SEM, mg): no DSS, 83.8 +/- 15.8; DSS, 159.5 +/- 6.3 (P < 0.001). In a separate set of animals, the ratio (R) of A(contact) to anatomic area in each plane was measured as in the previous study R(mean) (mean +/- SEM) and equaled 0.466 +/- 0.075, no DSS; 0.837 +/- 0.074, with DSS. The ratio of MTAC (1.52) and protein loss (1.90) approximate the ratio of R(mean(S)) (1.78). Because MTAC = mass transfer coefficient (MTC) x A(contact), small peritoneal transport chambers were used to determine MTC for (14)C-mannitol and fluorescein isothiocyanate-albumin. MTC(mannitol) did not change significantly with the addition of DSS. MTC(albumin) (cm/min x 10(4), mean +/- SEM) equaled 1.47 +/- 0.45 without DSS and 1.78 +/- 0.52 with DSS (P < 0.04). It was concluded that DSS increases the mass transfer rates of mannitol and protein by increasing A(contact), whereas protein transport is further augmented by an apparent increase in the barrier permeability to protein. (+info)
Circular dichroic properties and average dimensions of DNA-containing reverse micellar aggregates.
With the aim of investigating the compartmentation of nucleic acids and surfactant aggregates, we have studied the circular dichroic properties of DNA solubilized in reverse micelles. DNA incorporated in AOT/isooctane reverse micelles (AOT=bis-2-ethyl-hexyl sodium sulfosuccinate) assumes an anomalous circular dichroism (CD) spectrum with the characteristic features of a psi spectrum. Older literature observations could therefore be confirmed that attribute these spectral changes to the fact that the reverse micelles induce the formation of a condensed form of DNA. A dynamic light scattering (DLS) characterization of the DNA-containing micellar solutions was carried out, and three populations of aggregates in a polar solvent are observed, with an average radius centered at 5, 100 and 1000 nm, respectively, all three containing DNA. Several forms of DNA, including a plasmid, have been investigated. The formation of 1 microm-large aggregates depends on the DNA concentration and such aggregates disappear in the course of a few hours. Conversely, the 100 nm aggregates are stable for at least 1 day and contain DNA in a normal spectral state at low concentration and in a condensed form-it is the characteristic psi spectrum-in a higher concentration range. The solubilization of DNA in reverse micelles brings about unexpected larger structures in hydrocarbon solution, and whereas the very large component can be with all likelihood be attributed to clusters of smaller reverse micelles, the components at 100 nm radius appear to be a quite stable and characteristic feature of DNA-containing reverse micelles. (+info)
Stabilisation of tyrosinase by reversed micelles for bioelectrocatalysis in dry organic media.
The enzymatic and bioelectrocatalytic activity of tyrosinase from mushrooms was studied in a system of reversed micelles formed by Aerosol OT (AOT) in hexane. The optimal catechol oxidising activity of tyrosinase incorporated in reversed micelles was found at a hydration degree of w(0)=25. The catalytic activity was comparable with tyrosinase activity in aqueous media. When immobilized at an Au electrode, either directly or in reversed micelles, tyrosinase exhibited a similar efficiency of the bioelectrocatalytic reduction of O(2) mediated by catechol; however, a rapid decrease in the activity correlated with the destruction of reversed micelles and/or the removal of tyrosinase from the electrode surface. The system containing tyrosinase in reversed micelles with caoutchouk, spread on the surface of the Au electrode and successively covered with a Nafion membrane layer, was found to result in stable tyrosinase-modified electrodes, which were resistant to inactivation in dry acetonitrile. The proposed technique offers possibilities for further development of highly active and stable surfactant/enzyme-modified electrodes for measurements carried out in organic solvents. (+info)
Application of active-phase plot to the kinetic analysis of lipoxygenase in reverse micelles.
A new plot for explaining the complex expression of the enzymic activity in reverse micelles has been developed as an extension of the theoretical model described by our group [Bru, Sanchez-Ferrer & Garcia-Carmona (1990) Biochem. J. 268, 679-684]. The plot describes the changes in the relative volume, amount of enzyme (mumoles), enzyme concentration (microM) and substrate concentration (microM) in the phase where the enzyme is active. To illustrate the usefulness of this plot, the complex activity of soya bean lipoxygenase in reverse micelles acting on its interfacial substrate, octadecadienoic acid, was studied. It showed the key parameters ruling the activity profiles of lipoxygenase with respect to micelle size (omega 0), micelle concentration (theta) and the substrate/surfactant molar ratio (rho), which have never been described before. (+info)
Preparation and physicochemical characterization of dioctyl sodium sulfosuccinate (aerosol OT) microemulsion for oral drug delivery.
The performance of dioctyl sodium sulfosuccinate (aerosol OT) in the development of a pharmaceutically acceptable, stable, self-emulsifying water continuous microemulsion with high dilution efficiency was assessed. A pseudoternary microemulsion system was constructed using aerosol OT/medium-chain triglycerides with oleic acid/glycerol monooleate and water. The model microemulsion was characterized with regard to its electroconductive behavior, eosin sodium absorption, interfacial tension, and droplet size measurements after dilution with water. The percolation transition law, which makes it possible to determine the percolation threshold and to identify bicontinuous structures, was applied to the system. The interfacial tension changes associated with the microemulsion formation revealed ultralow values up to 30% oil at a surfactant/cosurfactant ratio of 3:1. Moreover, the investigated particle size and polydispersity using photon correlation spectroscopy after dilution with excess of the continuous phase proved the efficiency of the microemulsion system as a drug carrier that ensures an infinitely dilutable, homogeneous, and thermodynamically stable system. (+info)
Regulation of the supramolecular structure and the catalytic activity of penicillin acylase from Escherichia coli in the system of reversed micelles of Aerosol OT in octane.
The properties of penicillin acylase from E. coli solubilized by hydrated reversed micelles (RM) of Aerosol OT in octane were studied. The dependence of catalytic activity on the hydration degree, a parameter which determines the size of the micelle inner cavity, has a curve with three optima, each one corresponding to the enzyme functioning either in a dimer form (wo = 23) or in a form of separate subunits, a heavy one, beta, and a light one, alpha (wo = 20 and 14, respectively). The reversible dissociation of the enzyme was confirmed by ultracentrifugation followed by electrophoresis. (+info)
Can clinical trials requiring frequent participant contact be conducted over the Internet? Results from an online randomized controlled trial evaluating a topical ointment for herpes labialis.
BACKGROUND: The Internet has tremendous appeal for conducting randomized clinical trials and may be especially applicable to trials requiring frequent participant contact. Trials of cold sore remedies, for example, often require daily clinic visits during outbreaks, imposing substantial burden on participants. An Internet-based randomized clinical trial design may reduce this burden, permitting frequent symptom reports with considerably less effort. OBJECTIVE: To evaluate the feasibility of a Web-based randomized clinical trial requiring frequent participant interaction, using a 6-month, double-blind, randomized, placebo-controlled pilot trial of a topical ointment containing dioctyl sodium sulfosuccinate (DSS) (Zilex; Meditech Pharmaceuticals, Inc, Scottsdale, Arizona, USA) intended for treatment of recurrent herpes labialis. A secondary objective was to obtain preliminary data on effectiveness outcomes, to assist in planning a fully-powered trial of DSS. METHODS: Adults with physician-confirmed herpes labialis were recruited to apply to the trial. Eligible applicants were randomized to DSS or placebo, mailed to them upon enrolment with instructions to apply topically every 2 hours for the duration of every cold sore outbreak. Participants were instructed to complete online questionnaires at 2-week intervals and, at the initiation of a cold sore, daily "outbreak questionnaires" until outbreak termination. Feasibility outcome measures included trial participant characteristics, frequency of cold sores, participant retention and adherence (to study medication), and data completeness. Treatment effectiveness outcome measures included outbreak duration, days to crust formation, and pain. RESULTS: Of the 292 individuals applying, 182 screened eligible; 32 participants with confirmed herpes labialis enrolled in the trial. 16 were randomized into the verum group and 16 into the placebo group. 29 (91%) participants completed the trial. During the trial, 34 outbreaks were reported among 23 (72%) participants, resulting in a cold sore incidence rate of 19.8 per 100 person-months of observation. Online data were available for 32 outbreaks; the absence of a resolution date made it impossible to accurately calculate the duration of 12 (38%) outbreaks. Although the DSS treatment group had a shorter mean outbreak duration (6.6 vs 7.7 days, P =.2) and fewer mean days to crust formation (3.5 vs 4.9, P =.1), these differences did not reach statistical significance. The DSS group has statistically significant lower mean pain scores (3.1 vs 7.6, P =.04), but participants in this group also consumed more acetaminophen tablets than the placebo group (1.1 versus 0.5, P=.55). Adherence to medication was similar in both groups: 7 (50%) of the verum group reported using the cream as directed compared to 6 (46.2%) in the placebo group; (P =.8). CONCLUSIONS: We efficiently recruited participants and achieved high overall retention rates. However, participant adherence to the daily outbreak visit schedules was low and only 7 (50%) participants used the cream as directed. These limitations could be addressed in future Internet-based studies by using Personal Digital Assistants (PDAs), using reminder devices, and providing incentives. By enhancing participant adherence, clinical trials requiring frequent participant contact may be feasible over the Internet. (+info)