KINETIC-ANALYSIS OF THE MITOCHONDRIAL QUINOL-OXIDIZING ENZYMES DURINGDEVELOPMENT OF THERMOGENESIS IN ARUM-MACULATUM L

The dependence of the rate of oxygen uptake upon the ubiquinone (Q)-po ol reduction level in mitochondria isolated during the development of thermogenesis of Arum maculatum spadices has been investigated. At the alpha-stage of development, the respiratory rate was linearly depende nt upon the reduction level of the Q-pool (Qr) both under state-3 and -4 conditions, Progression through the beta/gamma to the delta-stage r esulted in a non-linear dependence of the state-4 rate on Qr. In the d elta-stage of development, both state-3 and -4 respiratory rates were linearly dependent upon Qr due to a shift in the engagement of the alt ernative oxidase to lower levels of Qr. Western blot analysis revealed that increased alternative oxidase activity could be correlated with expression of a 35 kDa protein. Respiratory control was only observed with mitochondria in the alpha-stage of development, At the beta/gamma -stage of development, the addition of ADP resulted in a significant o xidation of the Q-pool which was accompanied by a decrease in the resp iratory rate. This was due either to decreased contribution of the alt ernative pathway to the overall respiratory rate under state 3 or by d eactivation of succinate dehydrogenase activity by ADP. Cold-storage o f the spadices at the beta-stage of development led to increased activ ity of both the cytochrome pathway and succinate dehydrogenase, withou t any change in alternative oxidase activity. Results are discussed in terms of how changes in the activation level of the alternative oxida se and succinate dehydrogenase influence the activity and engagement o f the quinol-oxidizing pathways during the development of thermogenesi s in A. maculatum.