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Published on December 24, 2008; 10.1104/pp.108.129247

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Received September 3, 2008
Accepted December 15, 2008

REACTIVE OXYGEN SPECIES PRODUCTION BY POTATO TUBER MITOCHONDRIA IS MODULATED BY MITOCHONDRIALLY BOUND HEXOKINASE ACTIVITY

Juliana Camacho-Pereira , Laudiene Evangelista Meyer , Lilia Bender Machado , Marcus Fernandes Oliveira , and Antonio Galina *

From Instituto de Bioquimica Medica, Programa de Biofisica e Bioquimica Celular and Programa de Biologia Molecular e Biotecnologia, Universidade Federal do Rio de Janeiro, Laboratorio de Bioenergetica e Fisiologia Mitochondrial; Av. Brigadeiro Trompowsky, s/n, CCS, Bloco D, sub-solo sala D-013, Cidade Universitaria, , Rio de Janeiro, RJ, 21941-590. Brazil

* Corresponding author; email: galina{at}bioqmed.ufrj.br.

Potato tuber (Solanum tuberosum) mitochondria (PTM) have a mitochondrially bound hexokinase (mt-HK) activity that exhibits a pronounced sensitivity to ADP inhibition. Here we investigated the role of mitochondrial hexokinase activity in potato tuber mitochondria reactive oxygen species generation. Mitochondrial hexokinase has a ten fold higher affinity for glucose than for fructose (KMGlc = 140 µM versus KMFrc = 1375 µM). Activation of potato tuber mitochondria respiration by succinate led to an increase in H2O2 release that was abrogated by mitochondrial hexokinase activation. Mitochondrial hexokinase activity caused a decrease in the mitochondrial membrane potential ({Delta}{Psi}m) and an increase in oxygen consumption by potato tuber mitochondria. Inhibition of glucose phosphorylation by mannoheptulose or N-acetylglucosamine induced a rapid increase in H2O2 release. The blockage of H2O2 release sustained by glucose was reverted by oligomycin and atractyloside indicating that ADP re-cycles through the adenine nucleotide translocator and FoF1ATP synthase is operative during the mitochondrial hexokinase reaction. Inhibition of mitochondrial hexokinase activity by 60 to 70 % caused an increase of 50 % in the maximal rate of H2O2 release. Inhibition in H2O2 release by mitochondrial hexokinase activity was comparable to, or even more potent, than that observed for St-UCP activity. The inhibition of H2O2 release in potato tuber mitochondria was two orders of magnitude more selective for the ADP produced from the mitochondrial hexokinase reaction than for that derived from soluble yeast hexokinase. Modulation of H2O2 release and oxygen consumption by glucose and mitochondrial hexokinase inhibitors in potato tuber slices shows that hexoses and mitochondrial hexokinase may act as a potent preventive antioxidant mechanism in potato tubers.






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