446 



R. W. ESTABROOK 



results shown for cytochrome c from heart muscle where very slight changes 

 were seen when the sample was cooled in hquid nitrogen. The bacterial 

 cytochrome q shows much greater detail in the Soret region, at least five 

 absorption bands being apparent. 



Another series of r-type pigments which have been investigated are the 

 pigments cytochrome q of heart muscle and Cg of Azotobacter. These are 



460 490 520 550 

 Wovelength (rryj) 



Fig. 10. A comparison of the spectra of cytochrome c^ and c^. Curve A 

 represents the spectrum of cytochrome Cj obtained as a difference spectrum of 

 cytochrome c^ reduced by ascorbic acid minus the oxidized pigments of a heart 

 muscle DPNH-cytochrome c reductase. Curve B is the spectrum of cytochrome 

 C5 of Azotobacter vinelandii obtained with Na2S204 as reducing agent. Condition II. 



shown in Fig. 10. The spectrum of heart muscle cytochrome c is added as a 

 dotted curve to orient one in locating wavelengths. One of tiic first observa- 

 tions is that cytochromes (v, and c\ do not show a distinct splitting of the 

 alpha absorption bands. There is however, a pronounced splitting of the ft 

 bands. Although these two pigments have been derived from entirely 

 different organisms, i.e. heart muscle and Azotobacter vinelandii, they have 

 identical spectral characteristics in every way thus far measurable. It should 

 be mentioned, however, that there are differences in biological activity as 

 well as chemical properties between the two pigments. Cytochrome c^ 

 functions (Keilin and Hartree, 1955; Estabrook, 1958) between cytochrome Z? 



