REACTIONS INVOLVED IN OXIDATIVE PHOSPHORYLATION 267 



these two antibiotics on i\TPase induced by thyroid hormones, by valino- 

 mycin or by ageing (Fig. i). 



One manner of explaining the data would be to assume that two 

 reactions are involved in the ^'^O exchange reaction. 



X - I + Pi^OjH- ^ XisOPi^Og- + IH (la) 



Xi80pi803=+YH ;=^Xi80H + YPi803- (ib) 



YPO3 + ADP ^ YH + ATP (2a) 



If oligomycin blocked reaction (ib) and aurovertin blocked (la), each 

 would block the effect of DNP on ATPase since DNP acts above reaction 

 (la). We are then led to the conclusion that thyroid hormones, valinomycin 

 and ageing bring about ATP hydrolysis by catalyzing the hydrolysis of 

 XOPO3 . Their effect would thus be blocked by oligomycin but not by 

 aurovertin. 



There are some data which detract from the appeal of this scheme. 

 For example, valinomycin reverses the inhibition of mitochondrial 

 oxidation by aurovertin. But perhaps some uncoupling agents act at both 

 the DNP site and on XOPO.j'". We are now making a more detailed 

 comparison between aurovertin and oligomycin to determine whether they 

 act at two different sites or whether there is some other explanation for the 

 differential eifect of these antibiotics on various ATPase activities of 

 mitochondria. 



References 



1. Lardy, H. A., Johnson, D., and McMurray, W. C, Arch. Biochem. Biopliys. 

 78, 587 (1958). 



2. Lardy, H. A., and McMurray, W. C, Fed. Proc. 18, 269 (1959). 



3. Cohn, M., and Drysdale, G. W.,'}. biol. Chem. 2l6, 831 (1955); Boyer, P. D., 

 Falcone, A. B., and Harrison, W. H., Nature, Land. 174, 401 (1954). 



4. Wadkins, C. L., and Lehninger, A. L., J', biol. Cheyn. 233, 1589 (1958). 



5. Boyer, P. D., Luchsinger, W. W., and Falcone, A. B.,^. biol. Chem. 223, 405 



(1956). 



Discussion 



Lehninger: These are very interesting results. In the ^**0 exchange experi- 

 ments on dignitonin preparations we recently reported [Chan, Lehninger, and 

 Enns, J. biol. Cheyn. 235, 1790 (i960)] that our reaction scheme for oxidative 

 phosphorylation could not explain the higher incorporation of ^**0 from H.,^**© 

 into ATP than we were getting in the inorganic phosphate. The 2-stage mechanism 

 Dr. Lardy suggests might offer some possibiHty of explaining this ''^O exchange, 

 which otherwise can be explained only on a compartmentation basis. 



EsTABROOK : Is the arsenate stimulation of oxidation inhibited by oligomycin 

 as well as by aurovertin ? 



