Practice question

Outer membrane of mitochondrion is symmetric phospholipid bilayer containing cholesterol and porin channels that confer permeability to small solutes under five kilodaltons, distinguishing it from highly selective inner membrane bearing electron transport chain. Integral protein voltage-dependent anion channel VDAC, also called porin, forms nineteen-stranded beta-barrel with N-terminal alpha helix gating, isoforms VDAC1 most abundant, VDAC2, VDAC3 regulate metabolite exchange ADP ATP across intermembrane space, calcium transfer at mitochondria ER associated membranes interacting with IP3R via grp75, and scaffolding hexokinase II linking glycolysis to oxidative phosphorylation. Closure via interaction with tubulin regulates respiration. Cytochromes including cytochrome c are peripheral intermembrane space proteins loosely bound, bc1 complex, cytochrome c oxidase, ATP synthase all inner membrane, ribophorin proteins belong to rough ER oligosaccharyltransferase. Increased permeability through Bax Bak oligomers releasing cytochrome c triggers apoptosis, interaction with Bcl-xL modulates. Thus VDAC as hallmark outer membrane component governs metabolic flux and integrates survival signaling unlike respiratory complexes.