Properties of Cytoclironie b._. 



515 



(2:6-dichlorophenoIindophenol, DCIP), with 003 M sodium pyrophosphate - 

 HCl buffer at pH 8-0, 10^ m EDTA, 0-1 m DL-litliium lactate, and crystalline 

 cytochrome b^, (1 to 2 x 10~^ m). With ferricyanide, plots of E versus time 

 (T) were non-hnear, except for short time periods (up to 2 min) at high 

 ferricyanide concentrations (> 1-4 mM). The results conform approximately 

 with those expected for a first-order reaction. 



Essentially similar behaviour was observed with heart-muscle cytochrome 

 c as acceptor. With these acceptors, the first-order rate constant {k) was 

 estimated and different K^^ values for the acceptors were estimated from 

 plots of 1/A:S against 1/S. 



With DCIP, however, the reaction was substantially of zero order over the 

 range 0-22-0022 mM dye. Table 8 summarizes the apparent kinetic para- 

 meters for the various acceptors. 



In Table 8, the values given are called 'apparent kinetic parameters', since 

 the concentration of lactate was not varied, and there is a possibility that the 

 meaning of K,^ and V given in Table 8 do not have the usual significance 

 accorded to them. The true kinetic parameters for the reaction with heart- 

 muscle cytochrome c, as calculated from the studies reported below (mechan- 

 ism ///) are given in Table 9. These values are not so very difi'erent from the 

 apparent K^ and apparent V as given in Table 8. 



Table 8. Values of apparent Km and apparent V* for reaction of 



CYTOCHROME b.^ WITH VARIOUS HYDROGEN ACCEPTORS AT pH S'O AND 30°C 

 Results of Armstrong and Morton (1959); for experimental conditions, see text. 



V, maximum initial velocity at infinite concentration of reactants. 



Table 9. Kinetic parameters for the reaction of cytochrome 6. 



WITH cytochrome C 



Results of Armstrong and Morton (1959). 

 Determinations were carried out at pH 80 and 30°C. 

 For other experimental conditions, see text. 



