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Related Experiment Videos

Light-induced membrane potential and pH gradient in Halobacterium halobium envelope vesicles.

R Renthal, J K Lanyi

    Biochemistry
    |May 18, 1976
    PubMed
    Summary

    Light-induced proton movement across Halobacterium halobium vesicles generates a membrane potential and pH gradient. This proton-motive force, essential for cellular energy, is influenced by ion gradients and bacteriorhodopsin activity.

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    Area of Science:

    • Biophysics
    • Membrane Biology
    • Microbiology

    Background:

    • Halobacterium halobium utilizes bacteriorhodopsin for light-driven proton pumping.
    • Envelope vesicles from H. halobium can be used to study membrane transport and energy generation.

    Purpose of the Study:

    • To investigate the light-induced generation of membrane potential and pH gradients in H. halobium vesicles.
    • To quantify the proton-motive force and its components (electrical potential and pH gradient).

    Main Methods:

    • Utilized fluorescence spectroscopy with a cyanine dye to measure membrane potential.
    • Measured pH changes using a pH electrode or indicator.
    • Manipulated ion concentrations (K+, Na+) and used ionophores (valinomycin, gramicidin) to probe transport mechanisms.

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    Main Results:

    • Illumination caused a light-induced, reversible decrease in fluorescence, indicating membrane potential generation (inside negative).
    • The fluorescence decrease correlated linearly with membrane potential up to 90 mV.
    • Proton-motive force was dependent on Na+ and K+ gradients, with K+ being more permeable, leading to larger pH gradients and smaller electrical potentials.

    Conclusions:

    • The fluorescence decrease accurately reflects light-induced membrane potential in H. halobium vesicles.
    • H. halobium vesicles can generate substantial proton-motive forces (near -200 mV) crucial for cellular energy transduction.