On the regulation of Na+/H+ and K+/H+ antiport in yeast mitochondria: evidence for the absence of an Na(+)-selective Na+/H+ antiporter.
Unlike mammalian mitochondria, yeast mitochondria swell spontaneously in both NaOAc and KOAc. This swelling reflects the activity of an electroneutral cation/H+ antiport pathway. Transport of neither salt is stimulated by depletion of endogenous divalent cations; however, it can be inhibited by addition of exogenous divalent cations (Mg2+ IC50 = 2.08 mM, Ca2+ IC50 = 0.82 mM). Transport of both Na+ and K+ can be completely inhibited by the amphiphilic amines propranolol (IC50 = 71 microM) and quinine (IC50 = 199 microM) with indistinguishable IC50 values. Dicyclohexylcarbodiimide inhibits with a second-order rate constant of 1.6 x 10(-4) (nmol DCCD/mg)-1 min-1 at 0 degrees C; however, with both Na+ and K+ inhibition reaches a maximum of about 46%. The remaining transport can still be inhibited by propranolol. Transport of both cations is sensitive to pH; yielding linear Hill plots and Dixon plots with a pIC50 value of 7.7 for both Na+ and K+. These properties are qualitatively the same as those of the non-selective K+/H+ antiporter of mammalian mitochondria. However, the remarkable similarity between the data obtained in Na+ and K+ media suggests that an antiporter akin to the Na(+)-selective Na+/H+ antiporter of mammalian mitochondria, which is inhibited by none of these agents, is absent in yeast. In an attempt to reveal the activity of a propranolol-insensitive Na(+)-selective antiporter, we compared the rates of Na+/H+ and K+/H+ antiport in the presence of sufficient propranolol to block the K+/H+ antiporter. Between pH 4.6 and 8.8 no difference could be detected. Consequently, we conclude that yeast mitochondria lack the typical Na(+)-selective Na+/H+ antiporter of mammalian mitochondria.
Welihinda
A A
AA
Department of Biochemistry and Molecular Biology, Medical College of Ohio, Toledo 43699-0008.
Trumbly
R J
RJ
Garlid
K D
KD
Beavis
A D
AD
D017920:Antiporters / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*; D002413:Cations, Divalent / Q000494:pharmacology; D004024:Dicyclohexylcarbodiimide; D006863:Hydrogen-Ion Concentration; D008928:Mitochondria / Q000378:metabolism; D027961:Potassium-Hydrogen Antiporters; D011433:Propranolol / Q000494:pharmacology; D011803:Quinine / Q000494:pharmacology; D012441:Saccharomyces cerevisiae / Q000378:metabolism* / Q000648:ultrastructure; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism*
D017920:Antiporters; D002413:Cations, Divalent; D027961:Potassium-Hydrogen Antiporters; D017923:Sodium-Hydrogen Exchangers; D004024:Dicyclohexylcarbodiimide; D011433:Propranolol; D011803:Quinine