Enzyme turnover is essential for deactivation of F0F1-ATPase in plant mitochondria
1995
Chernyak, B.V. | Sigalat, C. | Diolez, P. | Haraux, F.
In potato tuber mitochondria, ATPase deactivates immediately after treatment with an uncoupler or with polyoxyethylene 9-lauryl ether (Lubrol), a non-ionic detergent. Deactivation was completely prevented by another non-ionic detergent, lauryldimethylamine oxide (LDAO). LDAO also induced slow reactivation of inactive ATPase formed in deenergized mitochondria. Freezing of the active state by LDAO was used to study the process of ATPase deactivation following deenergization in intact mitochondria. 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 mitochondria. The initial rate was close to the capacity for ATP synthesis but rapidly decayed. The rate of decay increased with the concentration of MgATP and no decay was observed in the presence of EDTA. The following conclusions were drawn. (1) Deenergization in itself is not sufficient for ATPase deactivation in plant mitochondria: enzyme turnover is also required. The probability of one enzyme to be deactivated at each turnover is much higher in potato tuber than in pea leaf organelles. (2) Enzyme turnover probably shifts the IF1-F1 complex from an active to an inactive form; the rate of deactivation indeed does not seem to be controlled by the binding of the inhibitory peptide. (3) The short-term effect (protection) and the long-term effect (reactivation) of LDAO on MF0MF1 may tentatively be used to titrate the activated versus total amounts of these enzymes in cells.
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