Related Experiment Video
Updated: Jun 23, 2026
08:39
Whole-cell Patch-clamp Recordings for Electrophysiological Determination of Ion Selectivity in Channelrhodopsins
Published on: May 22, 2017
Electrodichroism of purple membrane: ionic strength dependence
Biophysical Journal
|May 12, 2009
Summary
Purple membrane
Area of Science:
- Biophysics
- Membrane protein electrostatics
Background:
- Purple membranes contain bacteriorhodopsin, a light-driven proton pump.
- Understanding the electrostatics of purple membranes is crucial for bioenergetics.
Purpose of the Study:
- To investigate the electro-optical properties of purple membranes.
- To determine the permanent dipole moment, electrical polarizability, and retinal angle.
- To analyze the influence of electric fields and ionic strength on these parameters.
Main Methods:
- Measurement of purple membrane suspension dichroism in DC and AC electric fields.
- Analysis of dichroism as a function of electric field strength.
- Varied ionic strength using KCl and CaCl(2) solutions.
Main Results:
- A small decrease (approx. 2 degrees) in retinal angle observed between dark-adapted and light-adapted states.
- No significant changes in dipole moment, polarizability, or retinal angle during the photocycle.
- Retinal angle increased with ionic strength, attributed to a decreasing inner electric field.
- Polarizability comprises membrane and ionic cloud components, with the latter decreasing with ion concentration.
- Origin of ionic strength-dependent permanent dipole moment remains unclear.
Conclusions:
- Purple membrane electro-optical properties are sensitive to electric fields and ionic strength.
- The photocycle does not significantly alter key electrostatic parameters.
- Ionic strength influences the membrane's internal electric field and ionic cloud polarization.
More Related Videos
08:06Merging Ion Concentration Polarization between Juxtaposed Ion Exchange Membranes to Block the Propagation of the Polarization Zone
Published on: February 23, 2017
12:15Single Liposome Measurements for the Study of Proton-Pumping Membrane Enzymes Using Electrochemistry and Fluorescent Microscopy
Published on: February 21, 2019
Related Concept Videos
01:15Potentiometry: Membrane Electrodes
Membrane electrodes, also known as p-ion electrodes, use membranes that selectively interact with free analyte ions, generating a potential difference across the membrane. The resulting membrane potential, known as the asymmetry potential, is not zero even when analyte concentrations on both sides of the membrane are equal. The membrane's response is typically not selective to a single analyte but proportional to the concentration of all ions in the sample solution capable of interacting at the...
01:23Theory of Strong Electrolytes
The interionic forces of the strong electrolytes depend on the solvent's dielectric constant, which is the ability of a solvent to store electrical energy, based on its polarizability. and the solution's concentration. In high-dielectric solvents and in dilute solutions, weak electrostatic forces keep ions apart. However, in low-dielectric solvents or concentrated solutions, stronger interionic forces may cause ions to pair up as ionic doublets despite being fully ionized. The theory of strong...
01:30Ladder Diagrams: Redox Equilibria
Ladder diagrams are useful tools for understanding redox equilibrium reactions, especially the effects of concentration changes on the electrochemical potential of the reaction. The vertical axis in the redox ladder diagrams represents the electrochemical potential, E. The area of predominance is demarcated using the Nernst equation.
Consider the Fe3+/Fe2+ half-reaction, which has a standard-state potential of +0.771 V. At potentials more positive than +0.771 V, Fe3+ predominates, whereas Fe2+...
Consider the Fe3+/Fe2+ half-reaction, which has a standard-state potential of +0.771 V. At potentials more positive than +0.771 V, Fe3+ predominates, whereas Fe2+...
01:26What is an Electrochemical Gradient?
Adenosine triphosphate, or ATP, is considered the primary energy source in cells. However, energy can also be stored in the electrochemical gradient of an ion across the plasma membrane, which is determined by two factors: its chemical and electrical gradients.The chemical gradient relies on differences in the abundance of a substance on the outside versus the inside of a cell and flows from areas of high to low ion concentration. In contrast, the electrical gradient revolves around an ion’s...
01:12Ionic Strength: Overview
The ionic strength of a solution is a quantitative way of expressing the total electrolyte concentration of a solution. This concept was first introduced in 1921 by two American physical chemists, Gilbert N. Lewis and Merle Randall, while describing the activity coefficient of strong electrolytes. During the calculation of ionic strength (I or μ), all the cations and anions are considered. However, the concentration (c) of an ion with a greater charge number (z) has a greater contribution to...
01:30Anoxygenic Photosynthesis
Anoxygenic photosynthesis is a phototrophic process that captures light energy to drive carbon fixation without producing molecular oxygen. Unlike oxygenic photosynthesis, which utilizes water as an electron donor and releases oxygen, anoxygenic phototrophs use alternative electron donors such as hydrogen sulfide (H₂S), elemental sulfur (S⁰), or thiosulfate (S₂O₃²⁻). This process is carried out by diverse groups of bacteria, including purple bacteria, green sulfur bacteria, heliobacteria, and...