Reactions Involved in Oxidative Phosphorylation 

 as Disclosed by Studies with Antibiotics 



Henry Lardy 



Institute for Enzyme Research, 

 University of Wisconsin, Madison, TT'/V., U.S.A. 



Despite the great progress that has been made in understanding the 

 process of oxidative phosphorylation, the number of reactions involved and 

 the identity of all but a few of the reaction components remain unknown. 

 Most of the information extant has been gained from studies with intact 

 mitochondria. Ultimately the process must be examined in terms of the 

 individual enzymes involved and the reactions they catalyze. But while 

 isolation is in progress, new approaches to experiments with intact mito- 

 chondria may tell us how many components to look for. 



To this end we have examined nearly one hundred highly toxic anti- 

 biotics for possible effects on respiration and phosphate transfer by 

 mammalian mitochondria. Approximately lo",, of the compounds tested 

 have interesting effects on these processes (cf. [i]). 



Two of the antibiotics — oligomycin and aurovertin — at concentrations 

 of less than i fig. per ml. strongly inhibit mitochondrial oxidation of all 

 pyridine nucleotide-linked substrates. The inhibition is reversed by 2,4- 

 dinitrophenol (DNP) indicating that these two antibiotics block enzymes 

 involved in the energy-coupling mechanism, and have no effect on the 

 respiratory enzymes. 



Oligomycin was found [i] to inhibit the mitochondrial ATPase activity 

 induced by either DXP, thyroid hormones, deoxycholate or Ca + +. Since 

 dinitrophenol overcame the effect of oligomycin on respiration, and 

 oligomycin nullified the effect of dinitrophenol on ATPase, it seemed 

 possible that these two agents acted on the same enzymic site as com- 

 petitors. However, a direct test of this hypothesis demonstrated that 

 oligomycin did not act competitively in overcoming the effect of 

 dinitrophenol [2]. 



Aurovertin differs from oligomycin in its effect on ATPase (Fig. i). It 

 depresses, but does not completely inhibit, the ATPase activitv induced by 

 DXP, Ca ~ +, or TCAP. It has no effect on the ATPase induced by 

 Valinomycin, Triac, 0-AIe-Triac, DCA or ageing. Oligomycin overcomes 

 all these (Fig. i). 



