598 B, Chance 



and Hogness (1939) who studied the oxidation of ferrocytochrome c with 

 yeast peroxidase and peroxide. In fact, this interaction has been found to be 

 a general property of peroxidases (Chance, 1951). The velocity of this reaction 

 is so great that the size of the active centres involved was believed to exceed 

 that of the hacmatin groups, although more recent estimates suggest that an 

 active centre of about 5 sq. A for the reaction (see discussion on steric factors) 

 may still satisfy the experimental data (Beetlestone, 1960). 



c + Peroxidase Complex II ^ c + Peroxidase (1) 



Cytochioine Oxidase 



The reaction of ferrocytochrome c with cytochrome oxidase also appears 

 to be rapid. It may be studied in 'c-depleted' cytochrome chains, but this 

 system may not require a direct interaction of the soluble material with the 

 oxidase because of the possible presence of small residual amounts of bound 

 cytochrome c (Estabrook, 1959). Thus, most kinetic studies have been 

 carried out with cholate-treated fractions of the respiratory chain which may 

 contain cytochromes a and a^, but no detectable amounts of the other carriers 

 (Smith and Stotz, 1954; Yonetani, Takemori, Sekuzu and Okunuki, 1958). 

 Although considerable difficulties arise in kinetic studies of this material due 

 to the inhibition of the reaction by cytochrome c (Smith and Conrad, 1956), 

 the initial rate studies made some time ago indicated that a second order 

 velocity constant for the reaction could be as large as 10^ 1. x moles~^ x sec~^ 

 (Chance, 1952). 



10' 



(a + ^3)'" + c" c'" + {a + a^y (2) 



Independent kinetic data suggest that it is the cytochrome a component with 

 which cytochrome c interacts (Chance, 1955): 



a + c ^ c + a (3) 



This result clearly shows that reduced cytochrome c can react very rapidly 

 with the oxidase, suggesting that a special lipid form of cytochrome c is not 

 necessary for the electron transfer reaction (Green, 1959). 



The relevance of the result on the fragmented system depends upon 

 estimates of the effective concentration of the cytochromes as they are built 

 into the structure of the particle. Since spectrophotometric studies have 

 indicated that most respiratory chains consist of approximately equi-molar 

 amounts of the several cytochromes (Chance, 1952; 1958b), it is apparent 

 that the great majority of the carriers can exist in an 'assembly' that consists 

 of one each of its components (Note 1). Estimates of the concentration of 

 carriers in such an assembly are based upon the packing of haemoglobin in 

 the erythrocyte and values for the cytochromes of about 10"^ m are computed. 

 At these concentrations, a velocity constant of 10^ 1. x moles~^ x sec~^ would 



