Forms a channel through the mitochondrial outer membrane that allows diffusion of small hydrophilic molecules. The channel adopts an open conformation at low or zero membrane potential and a closed conformation at potentials above 30-40 mV. The open state has a weak anion selectivity whereas the closed state is cation-selective (By similarity). Highly expressed in flowers and at lower levels in roots and leaves. Highly expressed during the first days following germination and then decreases with time. Not induced by osmotic stress. Consists mainly of membrane-spanning sided beta-sheets. Belongs to the eukaryotic mitochondrial porin (TC 1.B.8.1) family.