Plant uncoupling mitochondrial protein activity in mitochondria isolated from tomatoes at different stages of ripening

In the present study we have observed a higher state of coupling in respiring mitochondria isolated from green as compared to red tomatoes (Lycopersicon esculentum, Mill.). Green tomato mitochondria produced a membrane potential (Delta Psi) high enough to phosphorylate ADP whereas in red tomato mitochondria, BSA and ATP were required to restore Delta Psi to the level of that obtained with green tomato mitochondria. This supports the notion that such uncoupling in red tomato mitochondria is mediated by a plant uncoupling mitochondrial protein (PUMP; cf, Vercesi et al., 1995). Nevertheless, mitochondria from both green and red tomatoes exhibited an ATP-sensitive linoleic acid (LA)-induced Delta Psi decrease providing evidence that PUMP is also present in green tomatoes. Indeed, proteoliposomes containing reconstituted green or red tomato PUMP showed LA uniport and LA-induced H+ transport. It is suggested that the higher concentration of free fatty acids (PUMP substrates) in red tomatoes could explain the lower coupling state in mitochondria isolated from these fruits.