Energy Transfer and Conservation in the Respiratory Chain 619 



Digital Computer Solutions 



Figure 7 illustrates electron transfer and phosphorylation functions of the 

 respiratory chain. This system consists of eight respiratory components 

 which may exist in the oxidized and reduced form, three intermediates of the 

 respiratory carriers which may exist in 'high-energy' forms, three transfer 

 intermediates, and a phosphorylation intermediate. The representation of 

 the kinetics of this system by an analogue computer is not practicable, but 

 recent work with the digital computer now makes such an approach possible 

 (Chance, 1959c, 1960b). 



I .The 'assembly' hypothesis has recently been termed the 'very warp and woof of the 

 membrane fabric' (Lehninger, 1959). 



2. This conclusion rests on the simplest hypothesis, namely that the non-phosphorylating 

 preparations have a generally similar electron transfer mechanism, but that some inter- 

 mediates, among them the substance I, lose their function upon preparation of the particles 

 by fragmentation of the mitochondria. 



3. It should be noted that this hypothesis is broadly based and includes that introduced 

 by Myers and Slater (1957) in which it is assumed that electron transfer in the phosphorylat- 

 ing system will not proceed in the usual fashion unless a substance (which they also label I) 

 is present. Here we are able to reconcile non-phosphorylating and phosphorylating electron 

 transfer: electron transfer can occur without the participation of I, but no phosphorylation 

 will result. With the participation of I, electron (or hydrogen) transfer is accompanied by 

 energy conservation, forming a compound that inhibits further electron transfer unless 

 reaction with the intermediate, X, occurs. This mechanism (cf. Equations 7-10) suggests that 

 the term 'phosphorylation' should not be applied to the respiratory chain, where the energy 

 conservation reactions do not appear to involve high-energy phosphate bonds. Further- 

 more, the sites at which 'phosphorylations' occur in the respiratory chain become rather 

 meaningless and the sites of inhibitory interactions take on a greater significance than 

 originally proposed by Chance and Williams (1955a). 



4. ADP and dicoumarol concentrations are sufficient to give approximately maximal 

 rates at 10°C. 



5. There appears to be a misunderstanding of ihe effect of reduction of the carriers upon 

 the rate of ^^P exchange or ATPase reaction. In the former case, binding of I as carrier ~' I 

 will decrease the exchange velocity in Equation 9. In addition, the increased carrier -^ I 

 concentration could easily drive more X into X -^ I (as in Equation 7 above). On this basis, 

 we have stated that under anaerobic conditions, X and I can be bound as X -->-' I and 

 carrier --^I and the exchange will be slow (Chance and Hollunger, 1957a; but cf. Slater, 

 1958, Equation 82, p. 250 et seq.). In the case of the ATPase reaction, there will be no 

 appreciable X ■-^ I concentration due to the action of the uncoupling agent (but cf. Slater, 

 1958, Equations 81 and 82) and the important eflFect of the carriers will be expressed in their 

 binding of I, probably in a low-energy form (carrier • I), thereby inhibiting the ATPase 

 sequence. It seems that these data support the idea that reduced carrier binds the ligand, I, 

 in accord with data on the ATP-jump (Schachinger, Eisenhardt and Chance, 1960) and also 

 with spectroscopic data (Chance and Williams, 1955b; Chance, 1959c). 



6. Added in proof. More recently it has been found that ATP can directly activate DPN 

 reduction in succinate-treated mitochondria and that an ATP/DPNH ratio as low as 2 can 

 be obtained (Chance, 1956; 1960a; Chance and Hagihara, 1960; Chance and Hollunger, 

 1960). 



7. Added in proof. The general case for an electrical circuit consisting of n resistive 

 elements and m interaction sites has been shown to be consistent with the crossover theorem 

 by Dr. Hattori in this laboratory. 



