CYTOCHROME C 347 



by Negelein and Gerischer (2024,2025) in Azotohacter. It predomi- 

 nates over cytochrome ai in Azotohacter, , Escherichia coli, Proteus 

 and Shigella dysenteriae (cf. also 962,1480,l]f81,31Jf9). 



Another cytochrome (ci) with absorption bands lying slightly more 

 toward the red has been found in heart muscle by Yakushiji and 

 Okunuki {31U)- This is confirmed by Theorell {2778). The oxidation- 

 reduction potential is said to lie between those of cytochrome c and 

 cytochrome b. 



3.3. Cytochrome c 



3.3.1. Isolation, Properties, and Estimation. Isolation. Of all 

 these compounds only cytochrome c has so far been isolated from 

 the cell and obtained in pure state. This is facilitated by its remark- 

 able stability. Although of protein nature, it is not denatured by 

 treatment with strong acids and is heat stable. Keilin {1284-, 1^77) 

 extracted cytochrome c from plasmolyzed yeast with sodium bisulfite 

 and dithionite and precipitated it with sulfur dioxide in the presence 

 of calcium chloride. Adsorption of cytochrome to kaolin was applied 

 by Zeile and Renter (3171). Oxidized cytochrome is readily adsorbed 

 on kaolin, while reduced cytochrome is not; the enzyme can thus be 

 easily eluted from the cytochrome adsorbate by reduction. This 

 difference in adsorbability is not yet explained. Yakushiji (314-1) 

 reports an isolation from higher plants and from algae, and Goddard 

 (1014) from commercial wheat germ. A purer cytochrome c was 

 obtained from ox or horse heart by Theorell (2764,2766) and Keilin 

 (1488,1500). Theorell used extraction with 0.1 N sulfuric acid, 

 adsorption to barium sulfate, acetone precipitation, and adsorption 

 on cellophane; while Keilin and Hartree extracted with trichloro- 

 acetic acid and purified by fractional ammonium sulfate precipitation. 

 Both methods lead to a cytochrome c with 0.34% iron. This corre- 

 sponds to a molecular weight of 16,500* (cf. Roche, Derrien, and 

 Cahnmann, 2315a). 



By submitting such preparations to electrophoresis, Theorell and 

 Akesson (2781,2782) found that below the isoelectric point of cyto- 

 chrome c (pH 10.05) they appeared to be homogeneous, while at a 

 higher /;H (10.68) a colorless protein or peptide could be separated 

 from the cytochrome c. The latter now contained more iron (0.43%). 

 By fractional precipitation with ammonium sulfate at pH 10, Keilin 

 and Hartree (1500) have recently obtained a cytochrome c with this 

 iron content. The catalytic activity is increased by these procedures. 



