Journal of Biological Chemistry
Volume 272, Issue 34, 22 August 1997, Pages 21104-21112
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MEMBRANES AND BIOENERGETICS
Properties of a Cyclosporin-insensitive Permeability Transition Pore in Yeast Mitochondria*

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Yeast mitochondria (Saccharomyces cerevisiae) contain a permeability transition pore which is regulated differently than the pore in mammalian mitochondria. In a mannitol medium containing 10 mm Pi and ethanol (oxidizable substrate), yeast mitochondria accumulate large amounts of Ca2+ (>400 nmol/mg of protein) upon the addition of an electrophoretic Ca2+ ionophore (ETH129). Pore opening does not occur following Ca2+ uptake, even though ruthenium red-inhibited rat liver mitochondria undergo rapid pore opening under analogous conditions. However, a pore does arise in yeast mitochondria when Ca2+ and Pi are not present, as monitored by swelling, ultrastructure, and matrix solute release. Pore opening is slow unless a respiratory substrate is provided (ethanol or NADH) but also occurs rapidly in response to ATP (2 mm) when oligomycin is present. Pi and ADP inhibit pore opening (EC50 ∼1 and 4 mm, respectively), however, cyclosporin A (7 μg/ml), oligomycin (20 μg/ml), or carboxyatractyloside (25 μm) have no effect. The pore arising during respiration is also inhibited by nigericin or uncoupler, indicating that an acidic matrix pH antagonizes the process. Pi also inhibits pore opening by lowering the matrix pH (Pi/OH antiport). However, inhibition of the ATP-induced pore by Pi is seen in the presence of mersalyl, suggesting a second mechanism of action. Since pore induction by ATP is not sensitive to carboxyatractyloside, ATP appears to act at an external site and Pi may antagonize the interaction. Isoosmotic polyethylene glycol-induced contraction of yeast mitochondria swollen during respiration, or in the presence of ATP, is 50% effective at a solute size of 1.0–1.1 kDa. This suggests that the same pore is induced in both cases and is comparable in size with the permeability transition pore of heart and liver mitochondria.

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*

This work was supported in part by United States Public Health Services Grant HL49182.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.