A SOLUBLE MITOCHONDRIAL PROTEIN INCREASES THE VOLTAGE DEPENDENCE OF THE MITOCHONDRIAL CHANNEL, VDAC

A soluble protein isolated from mitochondria has been found to modulate the voltage-dependent properties of the mitochondrial outer membrane channel, VDAC. This protein, called the VDAC modulator, was first found in Neurospora crassa and then discovered in species from other eukaryotic kingdoms. The modulator-containing fraction (at a crude protein concentration of 20-mu-g/ml) increases the voltage dependence of VDAC channels over 2-3-fold. At higher protein concentrations (50-100-mu-g/ml), some channels seem to remain in a closed state or be blocked while others display the higher voltage dependence and are able to close at low membrane potentials. By increasing the steepness of the voltage-dependent properties of VDAC channels, this modulator may serve as an amplifier in vivo to increase the sensitivity of the channels in response to changes in the cell's microenvironment, and consequently, regulate the metabolic flux across the outer mitochondrial membrane by controlling the gating of VDAC channels.