618 



B. Chance 



The solution of the differential equations for the reaction kinetics of the 

 components of a four-membered respiratory chain has been studied in some 

 detail (Chance et al., 1955) as have theorems relating the time sequence of 

 oxidation of the components to their order in the chemical sequence. Further- 

 more, the time sequence of reduction of the components is clearly indicated 

 by such studies, and theorems on the ordering of the values of t^ .^g. have 

 been derived in a recent dissertation (Higgins, 1959). It was on the basis of 

 preliminary forms of such theorems that the function of cytochrome b in 

 the non-phosphorylating respiratory chain could be rejected (Chance, 1952), 

 The theorem for the ordering of the half times of the 'off' reaction can be 

 simply stated : all intermediates (pij) involved in a linear reaction sequence 

 have their t^ .qq-. ordered, the /. .qq^. being greater the farther the intermediate 

 is from the substrate. Also, for conditions which appear to be characteristic 

 of the respiratory chain, the values of t^ .qq. show definite ordering properties. 



An example of extreme disordering in t^ -og-. is afforded by studies of 

 cytochrome b of the non-phosphorylating succinic oxidase preparation 

 (Chance, 1952). 



Not only does the analogue computer give steady-state solutions such as 

 those in Table 1 above, but dynamic responses are also available, as illus- 

 trated in Fig. 6 where the response of the respiratory chain of Table 1 to the 

 addition of ADP is indicated. It is seen that cytochromes a -{• a^ and c be- 

 come more reduced upon the addition of ADP while cytochrome b, pyridine 

 nucleotide, cytochrome c and DPNH become more oxidized. 



Og •— aj—— a'-Y-c"-*— (c,")-— b' 



sd- 



• succinate 



■ Conservation 

 ■rfp-j-DPNH-— /30h) Steps 



Energy 



DPNH~Ij 



3X-P + 3ADP--3ATP+3X 

 3X-4c.b.d^3X+3r 



Transfer, 

 Exchange, 



and 

 AT Rase 

 Reactions 



Fig. 7. A schematic diagram representing the electron transfer reactions, the 

 energy conservation sites, and the phosphorylation reactions of the respiratory 

 chain. The cytochrome components are indicated by the appropriate letter, and 

 fp and rfp represent respectively succinic dehydrogenases and DPNH dehydro- 

 genases. (MD-48) (Courtesy Journal of Biological Chemistry). 



