期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1974
卷号：71
期号：4
页码：1183-1187
DOI：10.1073/pnas.71.4.1183
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Recently proposed mechanisms of site II energy transduction that assign a key role to cytochrome b-566 are based on the finding that the apparent midpoint potential of b-566 in animal mitochondria increases by more than 250 mV upon addition of ATP [Chance et al. (1970) Proc. Nat. Acad. Sci. USA 66, 1175-1182]. However, since it has never been shown that the redox mediators used in the midpoint potential measurements equilibrate directly with b-566, the observed midpoint potential shift could merely reflect reversed electron transport. In mung bean mitochondria, the apparent midpoint potential of b-566 is known to be unaffected by addition of ATP [Dutton and Storey (1971) Plant Physiol. 47, 282-288]. In the present work, mung bean b-566 is shown to undergo an ATP-induced reduction similar to that observed for b-566 in animal mitochondria. However, in mung bean mitochondria the reduction is found to be rapidly relaxed by addition of redox mediator (phenazine methosulfate, PMS) and concomitantly PMS causes a marked, antimycinsensitive stimulation of ATPase activity. These results suggest that the ATP-induced reduction in mung bean mitochondria is due to reversed electron transport and that PMS can effectively short-circuit reversed electron transport in this system, bringing it close to equilibrium. Moreover, since mung bean and animal b-566 are identical in all other respects tested, the results support the idea that the apparent midpoint potential shift in animal mitochondria is also merely due to reversed electron transport, and that the mediators are now not effective enough to bring the system to equilibrium.
关键词：energy transduction ; potentiometric titration ; cytochrome b T
