ENZYME TURNOVER IS ESSENTIAL FOR DEACTIVATION OF F0F1-ATPASE IN PLANT-MITOCHONDRIA

In potato tuber mitochondria, ATPase deactivates immediately after tre atment with an uncoupler or with polyoxyethylene 9-lauryl ether (Lubro l), a non-ionic detergent. Deactivation was completely prevented by an other non-ionic detergent, lauryldimethylamine oxide (LDAO). LDAO also induced slow reactivation of inactive ATPase formed in deenergized mi tochondria. Freezing of the active state by LDAO was used to study the process of ATPase deactivation following deenergization in intact mit ochondria. Deactivation was slowed down by carboxyatractyloside (CATR) , which prevents ATP import into the matrix, and by ATPase inhibitors. ATP hydrolysis was also triggered by Lubrol with CATR-treated mitocho ndria. The initial rate was close to the capacity for ATP synthesis bu t rapidly decayed. The rate of decay increased with the concentration of MgATP and no decay was observed in the presence of EDTA. The follow ing conclusions were drawn. (1) Deenergization in itself is not suffic ient for ATPase deactivation in plant mitochondria: enzyme turnover is also required. The probability of one enzyme to be deactivated at eac h turnover is much higher in potato tuber than in pea leaf organelles. (2) Enzyme turnover probably shifts the IFI-F-1 complex from an activ e to an inactive form; the rate of deactivation indeed does not seem t o be controlled by the binding of the inhibitory peptide. (3) The shor t-term effect (protection) and the long-term effect (reactivation) of LDAO on MF(0)MF(1) may tentatively be used to titrate the activated ve rsus total amounts of these enzymes in cells.