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J. Biol. Chem., Vol. 276, Issue 44, 40502-40509, November 2, 2001

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Free Fatty Acids Activate a Vigorous Ca²⁺:2H⁺ Antiport Activity in Yeast Mitochondria^*

Patrick C. Bradshaw, Dennis W. Jung, and Douglas R. Pfeiffer

From the Department of Molecular and Cellular Biochemistry, Ohio State University Medical Center, Columbus, Ohio 43210

The accumulation and retention of Ca²⁺ by yeast mitochondria (Saccharomyces cerevisiae) mediated by ionophore ETH 129 occurs with a variable efficiency in different preparations. Ineffective Ca²⁺ transport and a depressed membrane potential occur in parallel, are exacerbated in parallel by exogenous free fatty acids, and are corrected in parallel by the addition of bovine serum albumin. Bovine serum albumin is not required to develop a high membrane potential when either Ca²⁺ or ETH 129 are absent, and when both are present membrane potential is restored by the addition of EGTA in a concentration-dependant manner. Respiration and swelling data indicate that the permeability transition pore does not open in yeast mitochondria that are treated with Ca²⁺ and ETH 129, whereas fatty acid concentration studies and the inaction of carboxyatractyloside indicate that fatty acid-derived uncoupling does not underlie the other observations. It is concluded that yeast mitochondria contain a previously unrecognized Ca²⁺:2H⁺ antiporter that is highly active in the presence of free fatty acids and leads to a futile cycle of Ca²⁺ accumulation and release when exogenous Ca²⁺ and ETH 129 are available. It is also shown that isolated yeast mitochondria degrade their phospholipids at a relatively rapid rate. The activity responsible is also previously unrecognized. It is Ca²⁺-independent, little affected by the presence or absence of a respiratory substrate, and leads to the hydrolysis of ester linkages at both the sn-1 and sn-2 positions of the glycerophospholipids. The products of this activity, through their actions on the antiporter, explain the variable behavior of yeast mitochondria treated with Ca²⁺ plus ETH 129.

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