Oligomycin A, also known as MCH 32, is an inhibitor of ATP synthase. Oligomycin A inhibits ATP synthase by blocking its proton channel (Fo subunit), which is necessary for oxidative phosphorylation of ADP to ATP (energy production). The inhibition of ATP synthesis by oligomycin A will significantly reduce electron flow through the electron transport chain; however, electron flow is not stopped completely due to a process known as proton leak or mitochondrial uncoupling. This process is due to facilitated diffusion of protons into the mitochondrial matrix through an uncoupling protein such as thermogenin, or UCP1.