Proton re-uptake partitioning between uncoupling protein and ATP synthase during benzohydroxamic acid-resistant state 3 respiration in tomato fruit mitochondria

The yield of oxidative phosphorylation in isolated tomato fruit mitochondri a depleted of free fatty acids remains constant when respiratory rates are decreased by a factor of 3 by the addition of n-butyl malonate. This consta ncy makes the determination of the contribution of the linoleic acid-induce d energy-dissipating pathway by the ADP/O method possible. No decrease in m embrane potential is observed in state 3 respiration with increasing concen tration of n-butyl malonate, indicating that the rate of ATP synthesis is s teeply dependent on membrane potential. Linoleic acid decreases the yield o f oxidative phosphorylation in a concentration-dependent manner by a pure p rotonophoric process like that in the presence of FCCP. ADP/O measurements allow calculation of the part of respiration leading to ATP synthesis and t he part of respiration sustained by the dissipative H+ re-uptake induced by linoleic acid. Respiration sustained by this energy-dissipating process re mains constant at a given LA concentration until more than 50% inhibition o f state 3 respiration by n-butyl malonate is achieved. The energy dissipati ve contribution to oxygen consumption is proposed to be equal to the proton ophoric activity of plant uncoupling protein divided by the intrinsic H+/O of the cytochrome pathway. It increases with linoleic acid concentration, t aking place at the expense of ADP phosphorylation without an increase in th e respiration.