410 



J. POSTGATE 



Table 2. Absorption spectra of cytochromes c and c^ 



(All wavelengths are in m/') 



Absoqjtion peaks of: 



Cytochrome c 



Cytochrome c^ 



Native protein (ferro) 

 Nitroso-protein (ferro) 

 CO-protein (ferro) 

 'Pyridine haemochrome' 

 'Porphyrin c or C3' (cone. HCI) 

 Haemin 



Chlorin formed with Na/Hg 

 Porphyrin with Na/Hg 

 (in dioxane) 



418 



415 

 415 



390* 



402\ 

 497/ 



520 

 53M 

 531-5 

 521-8 



530-21 

 566-51 



550-4 

 563-4 

 564-5 

 550-6 



553 



643 

 621-5t 



419 



415 

 413 



391 



402 \ 

 496-5 



525-2 

 532-5 

 530 

 521 



529-8) 

 556-8 



553-2 



563-5 



565 



551-8 



554 



643 

 621-5 



Haematohaemin 



t Mesoporphyrin 



The amino acids present in hydrolysates of cytochrome c^ have been 

 studied quahtatively by paper chromatography: those present are cystine, 

 histidine, lysine, arginine, methionine, phenylalanine, the leucines. Valine 

 was doubtful; diaminopimelic acid, hydroxyproline, and glutamme were 

 absent; the native protein gave no reaction for tryptophan. Quantitative 

 studies have not been undertaken. Compared with control hydrolysates of 

 commercial cytochrome c, hydrolysates of ^3 appeared to contain greater 

 quantities of histidine and cystine and less of threonine and lysine; in 

 addition, the commercial cytochrome c (Sigma) contained tryptophan, but 

 otherwise the amino-acid patterns were similar. 



These observations lead to the conclusion that cytochrome Cg is a protein 

 of the same general character and size as muscle cytochrome c, but having 

 two haem residues in the molecule instead of one. These haem groups are 

 bound to the apo-protein by thio-ether linkages as well as by co-ordination 

 to their central iron atom. 



Cytochrome c^ is associated in the cells with a soluble green pigment called 

 desulphoviridin, which has a strong absorption band at about 630 m/n. This 

 is not cytochrome 02', it undergoes no oxido-reduction reactions and de- 

 composes readily with acids, alkalis or heat to yield not a haem but a free 

 porphyrin. The latter has a strange spectrum recalling most closely that to be 

 expected for a water-soluble chlorin; it is blue-green in colour and is rapidly 

 photo-oxidized to a colourless derivative. 



Desulphoviridin is thus a kind of porphyroprotein. It has not been 

 purified, but concentrates freed of other strongly absorbing materials show 

 an a-band at 632 m/i, /5-band at 585 m//, and an unsymmetrical Soret peak 

 at 41 1 m^. The free prosthetic group, after chromatography on 'Florisil', is 

 an indicator and shows the following absorption bands in aqueous solution 



