PLANT PHYSIOLOGY , Vol 108, Issue 3 1035-1042, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Stimulation of the Alternative Pathway by Succinate and Malate
A. M. Wagner, CWM. van den Bergen and H. Wincencjusz
Department of Physiology and Biochemistry of Plants, Vrije Universiteit, De Boelelaan 1087, 1081 HV Amsterdam, The Netherlands (A.M.W., C.W.M.v.d.B.)
Stimulation of the cyanide-resistant oxidation of exogenous NADH in potato
(Solanum tuberosum L. cv Bintje) tuber callus mitochondria was obtained
with succinate, malate, and pyruvate. Half-maximal stimulation was observed
at a succinate or malate concentration of 3 to 4 mM, which is considerably
higher than that found for pyruvate (0.128 mM). No effect of succinate or
malate addition was found when duroquinone was the electron acceptor.
Duroquinol oxidation via the alternative pathway was poor and not
stimulated by organic acids. Under stimulating conditions, no swelling or
contraction of the mitochondria could be observed. Conversely, variation of
the osmolarity did not affect the extent of stimulation. However, the assay
temperature had a significant effect: no stimulation occurred at
temperatures below 16 to 20[deg]C. Membrane fluidity measurements showed a
phase transition at about 17[deg]C. Ubiquinone reduction levels were not
significantly higher in the presence of succinate and malate, but the
kinetics of the alternative oxidase were changed in a way comparable to
that found for stimulation by pyruvate. At low temperatures the alternative
oxidase displayed "activated" kinetics, and a role for membrane fluidity in
the stimulation of the alternative pathway by carboxylic acids is
suggested.
