Abstract: The Saccharomyces cerevisiae mitochondrial unspecific pore (ScMUC) is an uncoupling unspecific pore that shares some similarities with the mammalian permeability transition pore (mPTP). When open, both channels deplete ion and proton gradients across the inner mitochon-drial membrane. However, the role of mPTP is to reversibly open to protect cells against stress. If mPTP remains stuck in the open position the cell dies. In contrast, ScMUC is probably dedicated to deplete oxygen from the medium in order to kill competing organisms. Such O2 depletion would be better achieved if oxidative phosphorylation is at least mildly uncoupled. Still, when oxida-tive phosphorylation is needed ScMUC should be able to close. To test this, the reversible opening and closing of ScMUC in the presence of different effectors was tested in isolated mitochondria from S. cerevisiae. Evaluations were conducted at different incubation times, monitoring the rate of O2 consumption, mitochondrial swelling and the transmembrane potential. It was observed that ScMUC did remain reversibly open for minutes. A low energy charge (ATP/ADP) closed the chan-nel. In addition, high Ca2+ promoted closing and it was a highly powerful effector.