Properties of Cytochrome by 



509 



that at pH 6-5 probably reflects the dissociation of the riboflavin phosphate 

 group. 



Table 4. Principal absorption bands of crystalline cytochrome b^ 



AND OF ITS derivatives 



Wavelengths (A) are m//, extinction values (.E) are given for mM concentration of protein-bound haem ; 

 some are calculated values, and may be subject to slight revision. 

 Values are given for neutral pH at room temperature unless otherwise stated. 

 A. Bands in reduced compounds 



B. Bands in oxidized compounds 



* Broad band. t Shoulder only. 



1 Crystalline cytochrome b^ of Appleby and Morton (1954, 1959a) (flavohaemoprotein 

 containing deoxyribosepolynucleotide). 



2 Nucleotide-free cytochrome b., (Boeri et al., 1955; Armstrong and Morton, 1959) 

 (flavohaemoprotein). 



3 Enzymically-inactive haemo protein derivative of cytochrome Ag (Yamashita et al., 

 1957, 1958). The extinction values given for this compound are relative only and may be 

 subject to revision. 



* Transient intermediate ('lactate'-cytochrome 63 complex of Appleby and Morton 

 (1959b), see text). 



s Nucleotide-free cytochrome b., (Boeri el al., 1955) at temperature of liquid air (Linden- 

 mayer and Estabrook, 1958). 



Table 4 compares the extinction values and positions of the principle 

 absorption bands of reduced crystalline cytochrome ^2' of nucleotide-free 

 cytochrome ^2' and of the flavin-free haemoprotein derived from cytochrome 

 b^. In the fully reduced enzyme, the flavin appears to have Uttle influence on 

 the contribution of the haem group to the absorption spectrum (see also 

 Fig. 2). The high extinction values of the principal absorption bands of 

 cytochrome Zjg ^s compared with those of other cytochromes of group B 

 (see Morton, 1958, Table 5) therefore does not seem to be due to interaction 

 between the flavin and haem prosthetic groups. Moreover, if there were 

 direct interaction between the resonant systems of the fully reduced proto- 

 haem and flavin groups, the positions of the absorption bands of cytochrome 



