Antibiotic Pyrrolomycin as an Efficient Mitochondrial Uncoupler

Area of Science:

• Biochemistry
• Microbiology
• Pharmacology

Background:

• Pyrrolomycins C (Pyr_C) and D (Pyr_D) are antibiotics from Actinosporangium and Streptomyces.
• Their known antimicrobial mechanism involves bacterial membrane depolarization via protonophore action, uncoupling oxidative phosphorylation.

Purpose of the Study:

• To investigate the differential effects of Pyr_C and Pyr_D on isolated rat liver mitochondria and related membrane systems.
• To elucidate the structure-activity relationship concerning their protonophore properties and mitochondrial membrane interactions.

Main Methods:

• Experiments were conducted on isolated rat liver mitochondria, mitoplasts, inverted submitochondrial particles (SMPs), liposomes, and bilayer lipid membranes (BLMs).
• Mitochondrial respiration, membrane potential, and protonophore activity were measured using techniques like pyranine fluorescence and BLM electrophysiology.

Main Results:

• Pyr_C demonstrated higher activity in uncoupling intact mitochondria at submicromolar concentrations compared to Pyr_D.
• Pyr_D exhibited greater protonophore activity in SMPs, liposomes, and BLMs, particularly at pH values near its pKa.
• The differential activity was attributed to Pyr_C's enhanced ability to penetrate the outer mitochondrial membrane.

Conclusions:

• Pyrrolomycins C and D exhibit distinct activities based on the complexity of the membrane system.
• Pyrrolomycin C's efficacy against mitochondria is linked to its outer membrane penetration, while Pyrrolomycin D is a potent protonophore in simpler lipid environments.