A Hexokinase-initiated Inhibition of Oxygen Uptake in Tomato Fruit Mitochondria Uncoupled by Dinitrophenol.

The stimiulationi of oxygen uptake in. plant mitochondria uncotlupled by 2,4-dinitroplhenol (DNP) depends on aLdeniine ntucleotide in the absence of hexokinase (EC 2.7.1.1). Laties (9) observed this dependence with cauliflower bud miiitochondria oxidizing malate, while 'Wiskich anid Bonniier (13) reported a dotubling of the DNP-rate of oxygen tuptake bv adeninie nucleotide in sweet potato mitochondria oxidizinig succinate. Tomato fruit mitochondria also showed a dependenee onl adenine nucleotide in the presence of DNP and succinate and the absence of hexokinase (5). Heytler (7) reported a graduated suppressioni of oxygen uptake with increasing concentrations of the uncoupler, in-Cl-carbonyl cyanide phenylhydrazone, in the presence of hexokinase, in mouse liver mitochondria oxidizing succinate. Inhibition of succinate oxidation in rat liver and potato mitochondria in the absence of hexokinase depended on the concentration of uncoupler (12, 13). The inhibition of succinate oxidatioi niay be due to an inhibition of succinate dehyodrogenase (EC 1.3.99.1) by oxaloacetate (13). Wiskich and Boniner (13) suggested that ATP, which could be formed