An electron transfer dependent membrane potential in chromaffin-vesicle ghosts.

Area of Science:

• Biochemistry
• Cell Biology
• Neuroscience

Background:

• Adrenal medullary chromaffin-vesicle membranes house a transmembrane electron carrier.
• This carrier may supply reducing equivalents for dopamine beta-hydroxylase.
• An electron transfer system generates a membrane potential across chromaffin-vesicle membranes.

Purpose of the Study:

• To investigate the function and characteristics of the chromaffin-vesicle electron transfer system.
• To determine the role of this system in generating membrane potential.
• To explore the potential applications of this system in studying energy-linked processes.

Main Methods:

• Utilized resealed chromaffin-vesicle membranes (ghosts) with internal electron donors (ascorbic acid) and external electron acceptors (ferricyanide).
• Coupled the electron transfer system to cytochrome oxidase using cytochrome c to generate stable membrane potentials.
• Measured electron transfer rates via oxygen consumption and assessed the impact of inhibitors like cyanide.

Main Results:

• Ascorbic acid and isoascorbic acid effectively donate electrons.
• Ferricyanide causes a transient membrane potential, while cytochrome c coupling yields stable potentials.
• Stable potentials require cytochrome c, oxygen, and ferrocyanide, and are inhibited by cyanide.
• The generated membrane potential drives reserpine-sensitive norepinephrine transport.

Conclusions:

• The chromaffin-vesicle membrane contains an electron transfer system generating a functional membrane potential.
• This system is crucial for norepinephrine transport, confirming its location and activity.
• The electron transfer-driven membrane potential is a valuable tool for studying energy-linked processes in chromaffin vesicles.