[Permeability of yeast mitochondrial internal membrane: structure-activity relationship]

Area of Science:

• Mitochondrial biogenesis and function
• Membrane transport and bioenergetics
• Yeast cell biology

Background:

• The inner mitochondrial membrane's permeability to anions is crucial for cellular respiration and energy production.
• Understanding these properties in different states of mitochondrial differentiation (e.g., mitochondria, promitochondria, CAP-mitochondria) provides insights into membrane function.
• Investigating the role of ions like Mg2+ and specific transport mechanisms is key to elucidating mitochondrial bioenergetics.

Purpose of the Study:

• To investigate the relationship between anionic permeability and the function/structure of the inner mitochondrial membrane in Saccharomyces cerevisiae.
• To differentiate between electrogenic and electroneutral anion translocation mechanisms.
• To characterize the influence of energy state and Mg2+ on anion transport in various yeast organelle preparations.

Main Methods:

• Isolation of three yeast organelle types: mitochondria, promitochondria, and CAP-mitochondria.
• Swelling technique in isoosmotic potassium salts to assess membrane permeability.
• Determination of isotonic conditions and discrimination of electrogenic (valinomycin-induced) versus electroneutral (valinomycin and uncoupler-induced) translocation.

Main Results:

• Respiring mitochondria exhibit energy-dependent Cl- permeability, inhibited by Mg2+. Phosphate transport is electrogenic and mersalyl-sensitive, with Mg2+ restoring inhibition.
• Non-respiring mitochondria show Cl- impermeability, restored by ATP. Phosphate transport is partially electrogenic and mersalyl-sensitive.
• Promitochondria and CAP-mitochondria display Mg2+-dependent Cl- impermeability, with observed electrogenic (promitochondria) and electroneutral (CAP-mitochondria) phosphate transport, respectively. Mg2+ is essential for mersalyl sensitivity in CAP-mitochondria.

Conclusions:

• Mitochondrial inner membrane anion permeability is significantly influenced by the cell's energy status and the presence of Mg2+.
• Differentiation states of yeast mitochondria exhibit distinct patterns of anion transport, highlighting the dynamic nature of the inner mitochondrial membrane.
• The study elucidates specific roles for Mg2+ and mersalyl in regulating anion translocation, particularly phosphate, in various mitochondrial preparations.