In the presence of K+, addition of ATP or ethanol to yeast mitochondria triggers the depletion of the transmembrane potential (Delta Psi) and this is prevented by millimolar concentrations of phosphate (PO4). Different monovalent and polyvalent anions were tested for their protective effects on mitochondria from Saccharomyces cerevisiae. Only arsenate (AsO4) and sulfate (SO4) were as efficient as PO4 to protect mitochondria against the K+ mediated swelling, depletion of the Delta Psi, and decrease in the ratio of uncoupled state to state 4 respiration rates. Protection by PO4, SO4 or AsO4 was inhibited by mersalyl, suggesting that these anions interact with a site located in the matrix side. In addition, the effects of SO4 and AsO4 on the F1F0-ATPase were tested: both SO4 and AsO4 inhibited the synthesis of ATP following competitive kinetics against PO4 and non-competitive kinetics against ADP. The mersalyl sensitive uptake of (PO4)-P-32 was not inhibited by SO4 or AsO4, suggesting that the synthesis of ATP was inhibited at the F1F0-ATPase. The hydrolysis of ATP was not inhibited, only a stimulation was observed when AsO4 or sulfite (SO3) were added. It is suggested that the structure and charge similarities of PO4, AsO4 and SO4 result in undiscriminated binding to at least two sites located in the mitochondrial matrix: at one site, occupation by any of these three anions results in protection against uncoupling by K+; at the second site, in the F1F0-ATPase, AsO4 and SO4 compete for binding against PO4 leading to inhibition of the synthesis of ATP. (C) 2000 Elsevier Science B.V. All rights reserved.
Última actualización: 15/10/2018