Respiratory electron transfer activity in an asolectin-isooctane reverse micellar system

Area of Science:

• Biochemistry
• Bioenergetics
• Membrane Biophysics

Background:

• Bovine heart submitochondrial particles (SMP) are crucial for studying mitochondrial respiration.
• Organic solvent systems offer unique environments for investigating enzyme function.
• Understanding electron transfer mechanisms is vital for bioenergetics research.

Purpose of the Study:

• To investigate the functionality of the respiratory chain in bovine heart SMP solubilized in an organic medium.
• To identify the specific steps and limitations of electron transfer in this non-aqueous system.
• To explore methods for overcoming electron transfer blocks and restoring enzyme activity.

Main Methods:

• Solubilization of SMP in an asolectin-isooctane reverse micellar system.
• Spectroscopic and amperometric techniques to assess respiratory chain functionality.
• Enzyme kinetics studies varying electron donors, cofactors, and water concentration.

Main Results:

• Electron transfer from NADH to O2 was significantly impaired, arrested at the terminal oxidase step.
• Cytochrome oxidase, when reduced by ascorbate/NADH + TMPD, appeared trapped in a half-reduced state.
• Phenazine methosulfate (PMS) effectively bypassed the electron transfer block, restoring O2 uptake.
• Cytochrome oxidase activity in organic solvent showed high sensitivity to KCN and specific kinetics regarding PMS and water concentrations.

Conclusions:

• Electron transfer from NADH to O2 in organic media is blocked at the terminal oxidase.
• Cytochrome oxidase can exist in a non-reactive, half-reduced state in organic environments.
• PMS is a viable alternative electron mediator for reconstituting cytochrome oxidase activity in non-aqueous systems.
• Water concentration and PMS levels are critical parameters for optimizing cytochrome oxidase function in organic solvents.