Hacmoprotein of Purple Plwtusyntlictic Bacteria 



433 



class of compounds. I purposely left out cytochrome a^ (which combines with CO) 

 since it is so well established in the literature. 



I was not aware, of course, that Castor and Chance (/. biol. Chem. 234, 1587, 1959) 

 had also proposed a group name for these compounds (but had used another nomen- 

 clature) since their paper had not appeared. The name 'cytochrome d" for this class 

 was suggested provisionally since it was apparent that further information about 

 these pigments was required. I now feel that neither of these group names (viz. 

 'cytochrome d' and 'cytochrome o') should be further used and that only descriptive 

 classifications such as "RHP-type pigment of Chromatiiint' or 'CO-binding pigment 

 of M. pyogenes var. albus' should be used until the Commission on Enzyme Nomen- 

 clature has given a decision on cytochrome nomenclature. This would probably lead 

 to less confusion among biochemists generally. 



Cytochrome o 

 By B. Chance (Philadelphia) 

 Chance: In 1954, Lucile Smith and I discovered a photodissociable carbon monoxide 

 compound in several types of bacteria, the absorption bands of which were similar 



2.0 



• A. suboxydans 

 X M. pyogenes 

 var. albus 



■550 



400 440 480 520 



560 600 



Fig. 1. Photochemical action spectra for cytochrome o o[ A. suboxydans 



and M. pyogenes var. albus (from Castor and Chance, /. biol. Cliem. 217, 453, 



1955). Reprinted with permission of the Journal of Biological Chemistry. 



to haemoglobin. In view of this similarity and of Keilin and Tissieres' studies {Nature, 

 Land. Ill, 390, 1953) of haemoglobin in some micro-organisms, we proceeded 

 cautiously to ascribe a function to it. Not long thereafter, Castor, with his improve- 

 mept of Warburg's photochemical method, showed the compound to be a terminal 

 oxidase (Castor and Chance, /. biol. Chem. Ill, 453, 1955) and in 1959 named the 

 oxidase cytochrome o (Castor and Chance, /. biol. Chem. 234, 1587, 1959) (Fig. 1). 



