Mitochondrial permeability transition in yeast as a means to dissipate energy.
Victoriano Pérez-Vázquez, Andrés Rojas-Hernández, Sergio Guerrero-Castillo, Salvador Uribe
Inst de Fisiología Celular, Univ Nal Autónoma de México, Ciudad Universitaria, México, DF, 04510, Mexico
The yeast mitochondrial unspecific pore (YMUC) is probably equivalent to the mammalian permeability transition pore. The physiological meaning of mitochondrial depolarization in under debate. Functions ranging from programmed cell death to ion detoxification have been proposed. It was decided to characterize the function of the YMUC profiting from the potent molecular biology tools available. The opening of the YMUC is controlled by adenine nucleotides and phosphate (Pi). Thus, in the presence of high energy charge (high ATP and/or low Pi) the pore opens, oxidative phosphorylation uncouples and energy dissipates as heat. In contrast, when the energy charge is low, (ATP depleted and high Pi) the YMUC closes and the energy from the respiratory chain is used to synthesize ATP. In addition to the energy charge, another factor that seems to control the opening of the YMUC is calcium. Yeast mitochondria do not possess a high affinity system for the uptake of calcium, however, this cation closed the YMUC synergistically with magnesium and Pi. That is, at low concentrations of Pi (that do not close the YMUC), calcium is able to close it. The calcium site for the YMUC is on the external membrane, and probably is the porine. YMUC closing by calcium may be designed to enhance mitochondrial ATP output even when the energy charge is not very low. Both during cell division or mating a rise in cytoplasmic calcium has been observed.