Cytochrome b /// the Respiratory Chain 



583 



succinate, the y-band of cytochrome h was increased in intensity by 50-100% 

 (Fig. 4). The higher absorption was also found when antimycin was added 

 before the succinate. 



Fig. 4. Difference spectra of NaNOo-treated heart-muscle preparation (5-58 mg 

 protein/ml) reduced by succinate. Curve C, aerobic steady state minus oxidized, 

 showing partial reduction of cytochromes in the aerobic steady state. Curve A, 

 same as C in the presence of antimycin (009 /<g/mg protein). Curve D, anaerobic 

 steady state minus oxidized. Curve B, same as D in the presence of antimycin. 

 Curves A and C are partially corrected for light scattering by subtraction of the 

 absorbancy of C at 425 m/< (isosbestic point of reduced minus oxidized — Chance 

 (1958)) and Curves B and D by subtraction of the absorbancy of D at 425 m//. 

 Light path, 05 cm. Suspension medium as in Fig. 2. The inhibition by the 

 antimycin of the succinate oxidase activity was 31 %. 



In agreement with Chance (1958), the position of the peak of the y-band 

 of the difference spectrum (succinate -f antimycin minus succinate) was at a 

 slightly longer wavelength (432 m/j) than the band obtained with succinate 

 alone (431 mjj). 



As already mentioned, the extra absorption found by Chance (1958) at 

 435 m/^ and 556-566 mp, by the addition of Na.2S204 to a system already 

 containing succinate and antimycin can probably be ascribed to transfor- 

 mation of metmyoglobin and oxymyoglobin to myoglobin. It is our view 

 that the data of Chance and ourselves provide evidence for the presence of 



