C. Deswarte et al., PROTONOPHORIC ACTIVITY OF EUTYPINE, A TOXIN FROM EUTYPA-LATA, IN PLANT-MITOCHONDRIA, Archives of biochemistry and biophysics, 334(2), 1996, pp. 200-205
Eutypine is a toxin produced by Eutypa lata, the causal agent of the d
ying-arm disease of grapevine. We have previously shown that this toxi
n behaves as a lipophylic weak acid (pK = 6.2) and induces drastic cha
nges in both the respiration and energy balance of grapevine cells. In
the present study, the molecular mode of action of eutypine at the mi
tochondrial level, using methyl-eutypine, the unprotonable derivative
of the toxin, has been investigated. The effects of these molecules on
mitochondrial respiration and membrane potential were compared using
isolated mitochondria hom grapevine cells in suspension cultures or po
tato tuber mitochondria. Eutypine induces marked stimulation of oxygen
consumption and a depolarizing effect, while methyl-eutypine exhibits
a very small effect on both the rate of oxygen uptake and membrane po
tential. For high eutypine concentrations, a mixed effect correspondin
g to a direct inhibition of electron transport and uncoupling can be o
bserved. In addition, below 200 mu M, eutypine displays a linear relat
ionship between oxidation rate and membrane potential similar to that
of the classical protonophore carbonyl cyanide-m-chlorophenylhydrazone
(CCCP). However, unlike CCCP, eutypine induces a potential-dependent
proton conductance that can be due to the potential-dependent migratio
n of the dissociated form of the toxin across the membrane. It is conc
luded that eutypine uncouples mitochondrial oxidative phosphorylation
and decreases the ADP/O ratio in grapevine cells by increasing the pro
ton leaks via a cyclic protonophore mechanism. The physiological aspec
ts of these results are discussed. (C) 1996 Academic Press, Inc.