Cytochionics Cooled in Liquid Nitrogen 



AAl 



and c in mammalian tissues and has an oxidation-reduction potential of 

 about +0-145 V, while cytochrome c^ of Azotobacter has an oxidation- 

 reduction potential of about +0-300 V (Tissieres and Burris, 1956; Tissieres, 

 1956). In addition, cytochrome c^ is enzymatically active in particles of 

 Azotobacter, whereas it is not active in the heart muscle system. 



CYTOCHROMES OF THE 6-TYPE 



Cytochrome h^ 



A pigment which we have been most fortunate to have available (Note 7) 

 is cytochrome b^ from the halotolerant bacteria. As shown in Fig, 11, the 



A (m;i) 



Fig. 1 1 . Low temperature spectra of purified cytochrome A,i from halotolerant 

 bacteria. The upper curve represents the spectrum observed when purified 

 cytochrome b^ is diluted in 0-1 M phosphate buffer, pH 7-4 and reduced with 

 Na.jSoOi. The sample was then mixed with an equal volume of glycerol and the 

 spectrum recorded. The spectrum of the alkaline haemochrome of cytochrome 

 b^ was obtained in a similar manner except that the sample was diluted in 1 n 

 NaOH. Optical depth equals 1 mm. Condition II. 



a and /7 absorption bands of reduced cytochrome b^ show the most remarkable 

 splittiiig of any pigment yet observed. The two a absorption bands which are 

 observed at low temperature have their maxima about 6 nyx apart. Another 



