152 



A SYMPOSIUM ON RESPIRATORY ENZYMES 



Cytochrome c has, as compared with other biological systems, 

 a very high oxidation-reduction potential. As early as 1932 CooHdge 

 (22), using an impure preparation from yeast, reported a potential. 

 The rather unsatisfactory potential with the electrode could be 

 stabilized with hydroquinone. By adding oxidants or reductants to 

 a point where the spectrum of the cytoclirome changed, an Eo' of 

 + 0.260 V. at pH 7.0 was recorded. Lower values were obtained at 

 pH 5.0. In 1934 Green (23) determined the potential of an impure 



PROTEIN 



HX 



H.G 



rNJH2 COOH 

 CH 



r^Hp COOH 



C7H,oO±C±2H ± O 



— I 



S 



CH-CH 



CH2 

 COOH 



Figure 1. — Structure of cytochrome c 



