In the presence of K+, addition of ATP or ethanol to yeast mitochondria tri
ggers the depletion of the transmembrane potential (Delta Psi) and this is
prevented by millimolar concentrations of phosphate (PO4). Different monova
lent and polyvalent anions were tested for their protective effects on mito
chondria from Saccharomyces cerevisiae. Only arsenate (AsO4) and sulfate (S
O4) were as efficient as PO4 to protect mitochondria against the K+ mediate
d swelling, depletion of the Delta Psi, and decrease in the ratio of uncoup
led state to state 4 respiration rates. Protection by PO4, SO4 or AsO4 was
inhibited by mersalyl, suggesting that these anions interact with a site lo
cated in the matrix side. In addition, the effects of SO4 and AsO4 on the F
1F0-ATPase were tested: both SO4 and AsO4 inhibited the synthesis of ATP fo
llowing competitive kinetics against PO4 and non-competitive kinetics again
st ADP. The mersalyl sensitive uptake of (PO4)-P-32 was not inhibited by SO
4 or AsO4, suggesting that the synthesis of ATP was inhibited at the F1F0-A
TPase. The hydrolysis of ATP was not inhibited, only a stimulation was obse
rved when AsO4 or sulfite (SO3) were added. It is suggested that the struct
ure and charge similarities of PO4, AsO4 and SO4 result in undiscriminated
binding to at least two sites located in the mitochondrial matrix: at one s
ite, 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 comp
ete for binding against PO4 leading to inhibition of the synthesis of ATP.
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